Configure a week-based calendar

This article describes how to configure a week-based calendar for your Power BI Semantic Models. You configure your week-based calendar on the Power BI Reports Setup page, and your settings flow through to each connected semantic model.

Four concepts to consider

Think about your configuration in this order:

1. Define the Week Structure.
2. Define the Fiscal Year Anchor.
3. Define the Fiscal Boundary Rule.
4. Define the period pattern (445/454/544)

Define the week structure

Before you configure fiscal boundaries or 445 patterns, you must first define the week structure on the Power BI Reports Setup page by filling in the First Day of Week field. The week structure establishes the framework of the calendar.

Treat the First Day of Week setting as a foundational configuration that shouldn't change after you start to run reports. Changing the setting afterward:

• Changes historical fiscal year start dates.
• Changes week numbers for all historical data.
• Might change which years contain 53 weeks.
• Can break year-over-year period comparisons.

Define the fiscal year anchor

The anchor is the first day of the month specified in the First Month of Fiscal Calendar field on the Power BI Reports Setup page. It's the reference point that sets fiscal year boundaries.

In the following example, January is chosen as First Month of Fiscal Calendar. Therefore, the anchor for 2026 is Thursday, January 1.

Define the fiscal boundary rule

If you choose Weekly in the Calendar Type field, you can use the Weekly Type field to set the boundary rule (Nearest or Last). The rule determines how the anchor snaps to the week grid.

1. Nearest: Snap to the closest week boundary.
2. Last: Snap to the week that has the anchor.

Nearest rule

The following example describes how the Nearest rule works. The example assumes that fields are filled in as follows:

• The Weekly Type field is set to Nearest.
• The First Month of Fiscal Calendar field is set to January.
• The First Day of Week field is set to Sunday.

The anchor is Thursday, January 1, 2026.

Define the week grid for the Nearest rule

Because the First Day of Week field contains Sunday, the week grid runs from Sunday to Saturday. So, the week grid containing January 1, 2026 looks like:

Identify the two possible week boundaries

For the anchor (January 1), there are two possible starting points for your fiscal year:

• The previous week starting Sunday, December 28, 2025.
• The next week starting Sunday, January 4, 2026.

The Nearest rule chooses the boundary that's closest to the anchor.

Compare distances

The distance from January 1 to December 28 is four days backward. The distance to January 4 is three days forward. Because January 4 is closer, the fiscal year start is January 4, 2026.

Last rule

The following example describes how the Last rule works. The example assumes that fields are filled in as follows:

• The Weekly Type field is set to Last.
• The First Month of Fiscal Calendar field is set to January.
• The First Day of Week field is set to Sunday.

The anchor is Thursday, January 1, 2026.

Define the week grid for the Last rule

Because First Day of Week field contains Sunday, the week grid runs from Sunday to Saturday.

• Sunday is day 1
• Monday is day 2
• Tuesday is day 3
• and so on...

Find the start of the week containing the anchor

January 1, 2026 is a Thursday, so that week grid looks as follows:

Apply the Last rule

For the Last rule, the fiscal year begins on the first day of the week that contains the anchor date. Because January 1 is in the week that started December 28, the fiscal year starts on December 28, 2025.

Define the period pattern (445/454/544)

The next step is to determine how to group weeks into reporting periods by filling in the Quarter Week Type field:

• 445
• 454
• 544

The Quarter Week Type field specifies how to group weeks within each quarter. Each quarter contains 13 weeks that are distributed across three fiscal months according to the pattern you select.

All three patterns total 13 weeks per quarter (52 weeks per year, before any 53rd week adjustment).

Related information

Power BI Subscription Billing app
Overview of subscription billing