Need to start your week numbering from a specific date instead of January 1st? Whether you’re working on a project starting mid-year or want to reset the week count every month, here’s how to reset the week number in Google Sheets—without using scripts.
Let’s walk through how to reset the week number using both regular and array formulas.
Use Case 1: Start Week Number from a Specific Date (e.g., 01/04/2019)
Let’s say your project runs from 01/04/2019 to 31/12/2019, and you want April 1st to be week 1.
Normally, using =WEEKNUM(D3) for 01/04/2019 returns week 14, since it’s the 14th week of the year. To reset that to week 1 and continue from there:
Reset Week Number from a Specific Date – Non-Array Formula
=WEEKNUM(D3) - WEEKNUM($D$3) + 1This subtracts the week number of your project’s start date from each date, then adds 1 to begin counting from week 1.
Array Formula (Auto-fill for Entire Column):
=ArrayFormula(IF(LEN(D3:D), WEEKNUM(D3:D) - WEEKNUM($D$3) + 1, ))Use this when you have a list of dates (e.g., D3:D).
Change Week Start Day (e.g., Monday) Using ‘Type’ Argument
By default, WEEKNUM treats Sunday as the first day. To start weeks from Monday, use type 2:
=ArrayFormula(IF(LEN(D3:D), WEEKNUM(D3:D, 2) - WEEKNUM($D$3, 2) + 1, ))Use Case 2: Reset Week Number for Every Month
To restart week numbers at 1 for each new month:
Non-Array Formula:
=WEEKNUM(D3) - WEEKNUM(DATE(YEAR(D3), MONTH(D3), 1)) + 1Array Formula:
=ArrayFormula(IF(LEN(D3:D), WEEKNUM(D3:D) - WEEKNUM(DATE(YEAR(D3:D), MONTH(D3:D), 1)) + 1, ))Again, you can tweak the formula with a different type if your week starts on Monday or another day.
Use Case 3: Reset Week Number Based on Custom Week Start Day
Say your project starts on 18/07/2019, and you want the week to begin on Thursday (instead of Sunday or Monday). Here’s how:
- Find the weekday of the start date:
=TEXT(D3, "dddd")
Result:Thursday - Find the corresponding WEEKNUM type. For Thursday-Sunday weeks, use type 14.
Non-Array Formula:
=WEEKNUM(D3, 14) - WEEKNUM($D$3, 14) + 1Array Formula:
=ArrayFormula(IF(LEN(D3:D), WEEKNUM(D3:D, 14) - WEEKNUM($D$3, 14) + 1, ))This resets the week count using any custom start date and week structure.
More on the WEEKNUM Function
The formula that powers all these examples is WEEKNUM(date, [type]). The optional [type] lets you define which day the week starts. Here are some common ones:
- 1 – Sunday (default)
- 2 – Monday
- 11–17 – For weeks starting on Monday–Sunday
- 21 – ISO week number (Monday start, week 1 is the first week with a Thursday)
Refer to the official WEEKNUM Docs Help to explore all type options.
Conclusion
Whether you want to:
- Reset the week number from a custom date (like April 1st),
- Restart week numbers every month, or
- Define your own week start day (like Thursday),
You can do it efficiently in Google Sheets using simple formulas—no scripts needed.
Let me know in the comments if you have a specific case, and I’ll be happy to help!
