Building Week-Based and Custom Calendar Calculations in Power BI

Course: Microsoft Power BI Training

Topic: Building Week-Based and Custom Calendar Calculations

Course Link: Microsoft Power BI Training – JustAcademy

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1. Introduction to Week-Based and Custom Calendar Calculations

Calendar calculations are essential in Power BI because business reports often require more than standard daily, monthly, quarterly, and yearly analysis. Organizations may analyze performance by week, compare the same week across different years, use a financial calendar, or follow a custom reporting period.

Week-based and custom calendar calculations help transform date information into meaningful reporting periods. They are especially useful for sales reports, inventory monitoring, workforce planning, retail analytics, operational dashboards, and financial reporting.

For example, a retail business may define its reporting week as Monday through Sunday, while another organization may use Sunday through Saturday. A financial year may begin in April rather than January. These differences must be handled consistently so that measures, comparisons, and visualizations produce correct results.

Learning Objectives

• Understand calendar weeks and different week-numbering systems.
• Create week numbers, week-start dates, week-end dates, and week labels using DAX.
• Build custom calendars with financial years and custom reporting periods.
• Understand ISO week numbering and year-boundary situations.
• Sort week labels correctly in charts and tables.
• Apply week-based calculations to measures and business reports.
• Validate calendar logic and troubleshoot common date-related problems.

2. Understanding Calendar Weeks

A calendar week is a seven-day period used to group dates into reporting intervals. Although a week always contains seven days, the definition of its first day and its relationship with the calendar year can vary.

2.1 Common Week Definitions

2.2 Why Week Definitions Matter

Suppose a report groups dates by week number but the business expects Monday-to-Sunday weeks. If the calculation instead starts weeks on Sunday, transactions can appear in unexpected reporting periods. This can affect weekly totals, target comparisons, trend analysis, and year-over-year reporting.

Always confirm the organization's calendar rules before writing DAX formulas. A week number by itself is not enough to uniquely identify a week because the same number occurs in different years.

3. Preparing a Proper Date Table

A dedicated Date table provides a consistent foundation for week-based and custom calendar calculations. It should contain one row for every date in the required reporting range and should be related to the relevant fact table.

3.1 Create a Date Table with CALENDAR

The following DAX creates a Date table for a fixed range. Adjust the dates to match the reporting requirements.

DateTable =
CALENDAR(
    DATE(2023, 1, 1),
    DATE(2027, 12, 31)
)

The CALENDAR function returns a single-column table containing continuous dates from the specified start date through the end date, inclusive.

3.2 Create a Dynamic Date Table

If the model needs a date range based on existing transaction data, you can use the minimum and maximum transaction dates. Ensure the source column contains valid date values and that the range covers future planning requirements if necessary.

DateTable =
VAR MinimumDate =
    MINX(ALL(Sales), Sales[OrderDate])
VAR MaximumDate =
    MAXX(ALL(Sales), Sales[OrderDate])
RETURN
    CALENDAR(
        DATE(YEAR(MinimumDate), 1, 1),
        DATE(YEAR(MaximumDate), 12, 31)
    )

This example assumes a table named Sales and a date column named OrderDate. Replace these names with those used in your model. If the model includes budgets or future forecasts, extend the date range to cover those periods.

3.3 Mark the Date Table

1. Select the Date table in Power BI Desktop's Model view or Data view.
2. Open the table tools options.
3. Choose the option to mark the table as a date table.
4. Select the column containing unique, continuous date values.
5. Confirm that the table has no duplicate or missing dates within its intended range.

A well-defined Date table makes time-based modeling more reliable and helps keep calendar logic consistent throughout the report.

4. Extracting Week Information with DAX

After creating the Date table, add calculated columns to represent the week attributes required by the business. The formulas below assume that the Date table contains a column named Date.

4.1 Day of Week Number

DayOfWeekNumber =
WEEKDAY('DateTable'[Date], 2)

With the second argument set to 2, Monday is represented by 1 and Sunday by 7. This setting is useful when the organization follows a Monday-based week.

4.2 Day Name

DayName =
FORMAT('DateTable'[Date], "dddd")

This returns the full day name, such as Monday or Tuesday. For a short label, use "ddd". The displayed language can depend on the model's locale and formatting settings.

4.3 Week Number Starting on Monday

WeekNumber =
WEEKNUM('DateTable'[Date], 2)

The return type of 2 defines Monday as the first day of the week. This creates a Monday-based week-numbering calculation, but it is not automatically identical to ISO week numbering in every year-boundary case.

4.4 Week Number Starting on Sunday

SundayWeekNumber =
WEEKNUM('DateTable'[Date], 1)

The return type of 1 defines Sunday as the first day of the week. Use this only when it matches the reporting convention required by the organization.

4.5 Week Start Date for a Monday-Based Calendar

WeekStartDate =
'DateTable'[Date]
    - WEEKDAY('DateTable'[Date], 2)
    + 1

This calculation finds the Monday on or before each date. All dates in the same Monday-to-Sunday reporting week receive the same week-start date.

4.6 Week End Date

WeekEndDate =
'DateTable'[WeekStartDate] + 6

The week-end date is six days after the week-start date. For a Monday-to-Sunday calendar, this gives the Sunday at the end of the week.

4.7 Create a Readable Week Label

WeekLabel =
FORMAT('DateTable'[WeekStartDate], "dd MMM yyyy")
    & " - "
    & FORMAT('DateTable'[WeekEndDate], "dd MMM yyyy")

This produces labels such as 02 Jan 2023 - 08 Jan 2023. A label containing both dates is more descriptive than a week number alone.

5. Creating ISO Week-Based Calendar Calculations

The ISO 8601 week-date system is a standardized way to identify weeks. ISO weeks begin on Monday, and ISO week 1 is the week containing the first Thursday of the Gregorian calendar year. As a result, the ISO week-year can differ from the calendar year near New Year.

5.1 Why ISO Week-Year Is Important

For example, a date in early January may belong to the final ISO week of the previous ISO year. Likewise, a date in late December may belong to ISO week 1 of the following ISO year. Combining the calendar year with an ISO week number can therefore produce incorrect labels.

5.2 Calculate the ISO Week Start Date

ISOWeekStart =
'DateTable'[Date]
    - WEEKDAY('DateTable'[Date], 2)
    + 1

ISO weeks begin on Monday, so the Monday-based week-start formula can be reused.

5.3 Calculate the ISO Week Number

A common DAX approach derives the ISO week number from the Thursday in the same ISO week. The Thursday determines the ISO year associated with that week.

ISOWeekNumber =
VAR CurrentDate = 'DateTable'[Date]
VAR ThursdayOfWeek =
    CurrentDate
        - WEEKDAY(CurrentDate, 2)
        + 4
VAR FirstDayOfISOYear =
    DATE(YEAR(ThursdayOfWeek), 1, 1)
RETURN
    WEEKNUM(ThursdayOfWeek, 2)

The formula above uses the Thursday rule to associate a date with its ISO week-year and calculates the week number using a Monday-based week. The variable FirstDayOfISOYear is not required for the final expression and can be omitted. Always validate the result against known ISO calendar dates, particularly around December and January.

5.4 Calculate the ISO Week-Year

ISOWeekYear =
YEAR(
    'DateTable'[Date]
        - WEEKDAY('DateTable'[Date], 2)
        + 4
)

This returns the year of the Thursday in the date's week, which identifies the ISO week-year.

5.5 Create an ISO Year-Week Key

ISOYearWeek =
FORMAT('DateTable'[ISOWeekYear], "0000")
    & "-W"
    & FORMAT('DateTable'[ISOWeekNumber], "00")

The result may look like 2025-W03. Use both the ISO week-year and ISO week number when identifying a unique week.

Important: The ISO week number formula should be tested against authoritative ISO calendar examples before production use. Week numbering rules can differ between regional calendars and ISO 8601, and a generic WEEKNUM calculation is not sufficient by itself to guarantee ISO compliance in every environment.

6. Creating Custom Week Starts

Some organizations define their reporting week to start on a day other than Monday. Power BI can calculate week starts for any chosen day using the appropriate WEEKDAY return type.

6.1 Sunday-Based Week Start

WeekStartSunday =
'DateTable'[Date]
    - WEEKDAY('DateTable'[Date], 1)
    + 1

With return type 1, Sunday is day 1. The expression returns the Sunday on or before the current date.

6.2 Saturday-Based Week Start

WeekStartSaturday =
'DateTable'[Date]
    - MOD(
        WEEKDAY('DateTable'[Date], 2) - 6,
        7
    )

This expression returns the Saturday on or before the current date using Monday-based weekday numbering. Test it with sample dates before using it in business-critical reporting.

6.3 Configurable Week Start

If the organization needs to change the week start without rewriting every formula, define a parameter or configuration value and use a consistent calculation across the model. For example, a configuration table could store a number representing the desired first day of the week. A more complex implementation may use Power Query or a DAX expression driven by that configuration.

A configurable calendar is useful when multiple reporting teams follow different weekly definitions. However, a single Date table with one active week definition may not meet all needs simultaneously. In that situation, consider adding separate calendar attributes or maintaining separate calendar dimensions.

7. Building a Custom Financial Calendar

A financial calendar groups dates according to an organization's financial year rather than the standard January-to-December calendar year. In India, for example, many organizations use an April-to-March financial year, but the exact convention should always be confirmed for the business.

7.1 Financial Year Starting in April

FinancialYear =
VAR CurrentDate = 'DateTable'[Date]
RETURN
    YEAR(CurrentDate)
        + IF(MONTH(CurrentDate) >= 4, 1, 0)

This formula labels the financial year by its ending year. For example, April 2025 through March 2026 is labeled 2026. Some organizations instead label the same period as FY2025-26. Use the naming convention expected by the business.

7.2 Financial Year Label

FinancialYearLabel =
VAR CurrentDate = 'DateTable'[Date]
VAR StartYear =
    YEAR(CurrentDate)
        - IF(MONTH(CurrentDate) < 4, 1, 0)
VAR EndYear = StartYear + 1
RETURN
    "FY"
        & FORMAT(StartYear, "0000")
        & "-"
        & RIGHT(FORMAT(EndYear, "0000"), 2)

This returns labels such as FY2025-26 for dates between April 2025 and March 2026.

7.3 Financial Quarter

FinancialQuarterNumber =
INT(
    MOD(MONTH('DateTable'[Date]) - 4, 12) / 3
) + 1

The formula produces financial quarters beginning in April:

• Q1: April to June
• Q2: July to September
• Q3: October to December
• Q4: January to March

7.4 Financial Month Number

FinancialMonthNumber =
MOD(MONTH('DateTable'[Date]) - 4, 12) + 1

This assigns April the number 1, May the number 2, and March the number 12. Use the resulting number to sort financial month names in the intended order.

8. Building Financial Weeks and Week-Based Financial Years

Financial weeks require a clearly defined financial-year boundary and a rule for assigning the first week. A simple approach is to calculate the week number from the start of the financial year. This is different from ISO week numbering and should be documented as a custom business rule.

8.1 Calculate Financial-Year Start Date

FinancialYearStart =
VAR CurrentDate = 'DateTable'[Date]
VAR StartYear =
    YEAR(CurrentDate)
        - IF(MONTH(CurrentDate) < 4, 1, 0)
RETURN
    DATE(StartYear, 4, 1)

This returns 1 April of the financial year containing the current date.

8.2 Calculate Elapsed Days from Financial-Year Start

DaysFromFinancialYearStart =
DATEDIFF(
    'DateTable'[FinancialYearStart],
    'DateTable'[Date],
    DAY
)

This produces zero on the first day of the financial year, one on the second day, and so on.

8.3 Calculate a Seven-Day Financial Period Number

FinancialWeekNumber =
INT(
    'DateTable'[DaysFromFinancialYearStart] / 7
) + 1

This creates sequential seven-day blocks counted from 1 April. It does not necessarily align with Monday-to-Sunday calendar weeks. The first period starts on the financial-year boundary and can therefore begin on any weekday.

8.4 Align Financial Weeks to a Specific Weekday

If financial weeks must begin on Monday, Sunday, or another weekday, define whether the first financial week is allowed to be a partial week. Common policies include:

• Week 1 contains 1 April, even if it is a partial week.
• Week 1 begins on the first Monday on or after 1 April.
• Week 1 is the week containing a specific financial-year reference date.
• The organization uses a standardized retail calendar such as 4-4-5.

These policies can produce different week numbers for the same date. Document the chosen policy and validate it using boundary dates.

9. Creating Week Sort Columns

Text labels are useful for report readers, but text does not always sort chronologically. A label such as Week 1, Week 10, and Week 2 may sort alphabetically instead of numerically.

9.1 Create a Numeric Sort Key

YearWeekSort =
'DateTable'[ISOWeekYear] * 100
    + 'DateTable'[ISOWeekNumber]

This generates a numeric key such as 202503 for ISO week 3 of ISO year 2025. Ensure the year and week attributes use the same calendar convention.

9.2 Sort a Week Label in Power BI

1. Create a week label column and its numeric or date-based sort column.
2. Select the week label column in Data view.
3. Open the column tools options.
4. Choose Sort by column.
5. Select the corresponding sort key.
6. Use the label in charts, tables, slicers, and matrices.

The sort column should provide a one-to-one ordering for each distinct label. If the same label maps to multiple sort values, Power BI may reject the sort configuration or produce ambiguous results.

10. Creating Week-Based Measures

Once the Date table has been connected to the fact table, measures can summarize data by week. The examples below assume a Sales table with SalesAmount and OrderDate columns.

10.1 Total Sales

Total Sales =
SUM(Sales[SalesAmount])

When this measure is used with a week label from the Date table, it returns sales for each week in the current filter context.

10.2 Sales for the Current Filtered Week

Usually, no special week-specific DAX is required to calculate sales by week. Place the appropriate week attribute from the Date table on the visual axis and use the base measure.

Weekly Sales =
[Total Sales]

The date relationship and selected week field determine which transactions contribute to each result.

10.3 Previous Week Sales

One method is to calculate the previous week's date range from the selected week-start date. The measure below assumes that the report context contains one week-start date and that the Date table is related to the fact table.

Previous Week Sales =
VAR SelectedWeekStart =
    SELECTEDVALUE('DateTable'[WeekStartDate])
VAR PreviousWeekStart =
    SelectedWeekStart - 7
RETURN
    IF(
        NOT ISBLANK(SelectedWeekStart),
        CALCULATE(
            [Total Sales],
            REMOVEFILTERS('DateTable'),
            'DateTable'[Date] >= PreviousWeekStart,
            'DateTable'[Date] < PreviousWeekStart + 7
        )
    )

This measure intentionally returns blank when the current filter context does not identify exactly one week. Test the measure in visuals where one week is selected per data point. For multi-week totals, define the expected behavior explicitly rather than assuming a single week is selected.

10.4 Week-over-Week Change

Week over Week Change =
[Total Sales] - [Previous Week Sales]

10.5 Week-over-Week Percentage

Week over Week % =
DIVIDE(
    [Week over Week Change],
    [Previous Week Sales]
)

Format this measure as a percentage. The DIVIDE function safely handles a zero or blank denominator by returning blank unless an alternate result is specified.

10.6 Rolling Seven-Day Sales

A rolling seven-day measure calculates sales across a moving seven-day window ending on the selected date. This is different from sales for a fixed Monday-to-Sunday calendar week.

Rolling 7-Day Sales =
VAR EndDate =
    MAX('DateTable'[Date])
RETURN
    CALCULATE(
        [Total Sales],
        REMOVEFILTERS('DateTable'),
        DATESBETWEEN(
            'DateTable'[Date],
            EndDate - 6,
            EndDate
        )
    )

Use a continuous Date table so that the seven-day interval includes dates with no transactions. If the measure is intended to respect additional date filters or use a different window definition, adjust the filter logic accordingly.

11. Custom Calendar Structures: 4-4-5 and Similar Calendars

Retail businesses sometimes use a 4-4-5 calendar, where each quarter contains three periods consisting of four weeks, four weeks, and five weeks. This helps compare retail activity across periods with similar numbers of weekdays.

11.1 What Is a 4-4-5 Calendar?

• Each quarter normally has 13 weeks.
• The first period contains four weeks.
• The second period contains four weeks.
• The third period contains five weeks.
• Some years need an additional week to keep the retail calendar aligned with the business's chosen annual boundary.

Other common patterns include 4-5-4 and 5-4-4. These calendars are not equivalent to standard calendar months or ordinary ISO weeks.

11.2 Recommended Implementation

For a retail calendar, create a dedicated mapping table containing one row per date and the approved retail attributes, such as retail year, retail week, retail quarter, retail period, and period sort key. The mapping should come from the organization's official retail calendar or a clearly validated business rule.

This is often safer than trying to infer all retail-period boundaries from a simple week-number formula. An additional week can change the assignment of later periods and must be handled according to the approved calendar.

12. Creating Custom Calendar Columns in Power Query

Calendar columns can be created in DAX or Power Query. Power Query is useful when calendar attributes should be generated during data preparation and reused as part of the loaded Date table.

12.1 Example Power Query M Logic

The following example creates a Monday-based week-start column in an existing query that has a date column named Date.

= Table.AddColumn(
    PreviousStep,
    "WeekStartDate",
    each Date.StartOfWeek([Date], Day.Monday),
    type date
)

Replace PreviousStep with the actual name of the preceding query step. Power Query's Date.StartOfWeek function can use a specified day as the start of the week.

12.2 Add a Week Number in Power Query

= Table.AddColumn(
    PreviousStep,
    "WeekNumber",
    each Date.WeekOfYear([Date], Day.Monday),
    Int64.Type
)

Power Query and DAX week-number functions should not be assumed to use identical semantics for every calendar system. If the business requires ISO weeks, validate the week-year and week-number values at year boundaries.

12.3 DAX vs. Power Query

13. Building Relationships Between the Date Table and Fact Tables

Week calculations rely on a correctly modeled relationship between the Date table and the table containing transactions. If the relationship is missing or incorrect, weekly totals may be inaccurate or may repeat across periods.

13.1 Create the Relationship

1. Open Model view in Power BI Desktop.
2. Locate the Date table and the relevant fact table.
3. Connect DateTable[Date] to the transaction date column, such as Sales[OrderDate].
4. Use a one-to-many relationship, with the Date table on the one side and the fact table on the many side.
5. Check that the data types match and the Date table contains unique dates.
6. Confirm the relationship is active if it should filter the fact table by default.

13.2 Date and Time Values

If the transaction column contains both a date and a time, it may not match the Date table's date-only values. Create a date-only column in Power Query or another suitable transformation, then relate that column to the Date table.

13.3 Multiple Date Columns

A fact table may contain order date, shipment date, invoice date, and delivery date. One relationship can be active by default while other relationships are inactive or handled through separate role-playing Date tables. Choose the correct date relationship for each measure.

14. Working with Week-Based Filters and Slicers

Week fields can make reports easier to navigate, but the field used in the slicer should uniquely and clearly identify the intended reporting period.

14.1 Useful Slicer Fields

• Week start date
• Week end date
• Week label
• ISO year-week label
• Financial year and financial week
• Retail year and retail period

14.2 Avoid Ambiguous Week Numbers

A slicer containing only week numbers from 1 to 52 can combine data from multiple years. Include the calendar year or week-year in the selection when users need to identify a unique week.

14.3 Build a Weekly Trend Chart

1. Add a line chart to the report canvas.
2. Place the chronological week label or week-start date on the X-axis.
3. Add the relevant measure, such as Total Sales, to the Y-axis.
4. Sort the visual by the numeric sort key or week-start date.
5. Use year and category slicers as required.
6. Test the visual around year-end and weeks with no transactions.

15. Common Errors and Troubleshooting

16. Best Practices for Week-Based Calendar Design

• Confirm the week-start day and week-numbering convention with business stakeholders.
• Use a dedicated Date table with one row per date.
• Keep week-start and week-end dates available for clear reporting.
• Use a unique year-week key rather than week number alone.
• For ISO reporting, calculate both ISO week number and ISO week-year.
• Validate dates near the end of December and the beginning of January.
• Use explicit sort keys for week labels and financial periods.
• Keep custom calendar definitions documented and consistent across reports.
• Use an approved mapping table for 4-4-5 or other complex retail calendars.
• Test measures with single-week, multi-week, and no-selection filter contexts.
• Ensure the Date table covers historical transactions and required forecast periods.
• Avoid duplicating different calendar conventions in measures without clear naming.

17. Practical Exercise

Objective: Build a Power BI report that compares weekly sales across calendar and financial periods.

Exercise Requirements

1. Import a sales dataset containing order date, product, region, quantity, and sales amount.
2. Create a continuous Date table covering the entire reporting period.
3. Add day name, week start, week end, week number, week label, and year-week sort columns.
4. Create ISO week-year attributes if the reporting requirement calls for ISO weeks.
5. Create financial year, financial quarter, and financial month columns using the agreed fiscal-year start month.
6. Connect the Date table to the sales fact table.
7. Create a total sales measure and a previous-week sales measure.
8. Create a week-over-week change and percentage measure.
9. Build a weekly trend chart and add week, year, region, and product slicers.
10. Test the report using dates near New Year and the financial-year boundary.

Expected Outcome

The completed report should display weekly sales in chronological order, support filtering by calendar or financial periods, and produce consistent week-over-week comparisons. Week labels should be unambiguous, and date filters should correctly affect the sales measures.

18. Mini Project: Weekly Sales and Custom Calendar Dashboard

Create a dashboard for a business that wants to compare weekly performance across standard and financial calendars.

Dashboard Components

• KPI cards: Total sales, current selected-week sales, previous-week sales, and week-over-week percentage change.
• Weekly trend: A line chart showing sales by week-start date.
• Year comparison: A chart comparing sales by week-year using the organization's chosen week convention.
• Financial summary: A matrix showing financial year, financial quarter, financial month, and sales.
• Regional analysis: A bar chart comparing weekly sales across regions.
• Filters: Week, year, financial year, product category, and region.

Validation Checklist

• Verify that each Date table row represents one unique date.
• Verify that all fact-table dates fall within the calendar range.
• Check that every week label maps to the intended week start and end.
• Compare a sample of weekly totals with a manual calculation.
• Validate week-year assignment for dates near New Year.
• Confirm financial periods follow the organization's documented policy.
• Confirm all labels sort chronologically in visuals.

19. Interview Questions and Answers

Q1. What is a week-based calendar calculation in Power BI?

A week-based calendar calculation assigns dates to weekly reporting periods. It may include week number, week start, week end, week-year, and other custom weekly attributes.

Q2. Why is a week number alone not a unique identifier?

Week numbers repeat every year. A year-week key or a week-start date is needed to distinguish one week's data from another.

Q3. What is the difference between WEEKNUM and WEEKDAY?

WEEKNUM returns a week number within a year according to the selected convention. WEEKDAY returns a number representing the day of the week.

Q4. How do you calculate the start of a Monday-based week?

Subtract WEEKDAY(Date, 2) - 1 from the date. This returns the Monday on or before the specified date.

Q5. What is an ISO week-year?

The ISO week-year is the year assigned to a date by the ISO week-date system. It can differ from the calendar year around the beginning and end of the year.

Q6. Why should ISO week calculations be tested near New Year?

Some late-December dates belong to ISO week 1 of the following ISO year, while some early-January dates belong to the last ISO week of the preceding ISO year.

Q7. How do you create a financial year beginning in April?

Create a calculated column that increases the calendar year by one for dates in April or later if the financial year is labeled by its ending year. The exact label should match the organization's convention.

Q8. Why are sort columns important for week labels?

Text labels may sort alphabetically. A numeric or date-based sort column ensures that week labels appear in chronological order.

Q9. What is a 4-4-5 calendar?

It is a retail calendar pattern in which periods within each quarter typically contain four, four, and five weeks. It supports comparable retail reporting periods.

Q10. Should custom calendar logic be created in DAX or Power Query?

Either can be appropriate. Use Power Query when the logic belongs in data preparation and DAX when the logic belongs in the semantic model. Maintain one consistent definition and validate the results.

Q11. How can you calculate previous-week sales?

Identify the current week's start date, shift it back seven days, and calculate the measure over that previous seven-day range. The measure should explicitly handle contexts containing multiple weeks.

Q12. Why might a weekly sales measure repeat the same value across every week?

The Date table may not be related correctly to the fact table, the visual may use a field from the wrong table, or the measure may remove date filters unintentionally.

20. Quick Revision Checklist

• Understand the difference between calendar weeks, ISO weeks, and custom business weeks.
• Create a continuous Date table and mark it as a date table.
• Calculate week number, week start, and week end.
• Use week-year with week number when identifying a unique period.
• Calculate financial years and quarters according to the agreed fiscal start month.
• Create sort keys for readable week labels.
• Build and validate week-based measures using the correct Date table relationship.
• Use mapping tables for complex retail calendars.
• Test year boundaries, financial-year boundaries, and weeks with no transactions.

21. Conclusion

Building week-based and custom calendar calculations in Power BI allows analysts to organize dates according to real business reporting needs. By combining a reliable Date table with week-start and week-end dates, week-year attributes, financial calendar columns, and properly sorted labels, you can create more accurate and understandable weekly reports.

The most important principle is to define the calendar rules before implementing the calculations. Standard Monday-based weeks, ISO weeks, financial weeks, and retail calendars can assign dates to different periods. Use consistent definitions, validate edge cases, and ensure that the Date table relationships and measures reflect the intended reporting logic.

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