Weeks Calculator: Weeks and Days Between Two Dates

Pick two dates to see the gap in whole weeks and days, in decimal weeks, and the week number of the year for each date.

FreeNo sign-upRuns in your browserUpdated 2 Nov 2026
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Estimates only. Check important results before you rely on them.

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How to use this calculator

  1. Pick the first and the second date.
  2. Read the weeks and days at the top.
  3. See the decimal weeks and total days.
  4. Check the week number of each date.

The formula

Weeks = Days ÷ 7. Whole weeks = floor(Days ÷ 7), leftover days = Days mod 7. ISO week numbers count weeks from the week with the first Thursday.

Worked example

From 1 January 2026 to 2 November 2026 is 305 days, which is 43 weeks and 4 days, or 43.57 weeks. They fall in ISO weeks 1 and 45.

Understanding your result

The order of the dates does not matter. Week numbers follow ISO 8601, which starts the week on Monday and may differ from other calendars.

When to use it

  • Plan pregnancy, project or training weeks.
  • Count weeks to an exam or event.
  • Find the week number of a date.

Assumptions and limits

Counts calendar days only. The first date is not counted when finding the gap.

Frequently asked questions

How many weeks are between two dates?

Divide the number of days between them by 7.

What is an ISO week number?

The week of the year under ISO 8601, where weeks start on Monday and week 1 contains the first Thursday.

How many weeks are in a year?

52 weeks and 1 day, or 52 weeks and 2 days in a leap year.

Can the dates be in any order?

Yes. The calculator puts them in order.

Does it include the end date?

No. It counts the days between the dates.