Get a Date from Year & Week Number

Excel Formulas › Date & Time

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WEEKNUM turns a date into a week number — this is the reverse. Given a year and a week number, compute the actual calendar date the week starts on.

Quick formula: for a year in B1 and ISO week number in B2 (Monday start):
=DATE(B1,1,4) - WEEKDAY(DATE(B1,1,4),2) + 1 + (B2-1)*7
It finds the first ISO week’s Monday, then jumps forward (week−1) times seven days.

Functions used (tap for the full reference guide):

DATEWEEKDAY

The example

The Monday that begins each ISO week of 2026.

ABC
1YearWeekWeek starts
220261Mon 12/29/2025
3202610Mon 3/2/2026
4202626Mon 6/22/2026

The formula

The Monday that starts a given ISO week:

=DATE(B1,1,4) - WEEKDAY(DATE(B1,1,4),2) + 1 + (B2-1)*7 // 2026, week 26 → Mon 6/22/2026

How it works

Work back to the first week’s Monday, then add weeks:

  1. DATE(B1,1,4) lands on January 4, which is always inside ISO week 1 (the week containing the first Thursday) — a reliable anchor in every year.
  2. WEEKDAY(…,2) returns 1–7 with Monday = 1, so subtracting it (and adding 1) snaps back to that week’s Monday.
  3. (B2-1)*7 jumps forward the right number of weeks to reach the target week’s Monday.
  4. For a US-style (Sunday-start, week 1 = the week of Jan 1) convention, use =DATE(B1,1,1) - WEEKDAY(DATE(B1,1,1)) + 1 + (B2-1)*7.

Want any weekday of that week? Add an offset: +0 for Monday through +6 for Sunday. To get the week’s Friday, add 4 to the Monday result.

Try it: interactive demo

Live demo

Enter a year and ISO week number.

Week starts:

Variations

US (Sunday-start) week

Week 1 = the week of Jan 1:

=DATE(B1,1,1) - WEEKDAY(DATE(B1,1,1)) + 1 + (B2-1)*7

Any weekday of the week

Add 0 (Mon) to 6 (Sun):

=[week Monday] + 4 // Friday

Reverse check (date → week)

ISO week number of a date:

=WEEKNUM(A2, 21)

Pitfalls & errors

Week-numbering systems differ. ISO (Monday start, week 1 has the first Thursday) and US (Sunday start, week 1 has Jan 1) give different dates. Match the system your data uses.

Week 1 can start in December. ISO week 1 of 2026 begins Mon 12/29/2025 — that’s correct, not a bug.

Format as a date. The result is a serial number; apply a date format so it doesn’t show as 46000-something.

Practice workbook

📊
Download the free Get a Date from Year & Week Number practice workbook
A week-to-date converter with ISO and US conventions, weekday-offset and reverse-check variants, plus 4 challenges with answers. No sign-up required.

Frequently asked questions

How do I get a date from a week number in Excel?
For ISO weeks: =DATE(year,1,4)-WEEKDAY(DATE(year,1,4),2)+1+(week-1)*7 returns the Monday that starts the week. January 4 is always in ISO week 1, which makes it a reliable anchor.
Why does week 1 start in the previous December?
Under ISO rules, week 1 is the week containing the first Thursday, so it can begin in late December — e.g. ISO week 1 of 2026 starts 12/29/2025.
How do I get a US-style week date instead?
Use =DATE(year,1,1)-WEEKDAY(DATE(year,1,1))+1+(week-1)*7, where week 1 contains January 1 and weeks start on Sunday.

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Related formulas: ISO week number · First & last day of month · Next weekday

Function references: DATE · WEEKDAY