Week Calculator
This week calculator counts the weeks between two dates and moves a date forward or back by a number of weeks. Example: from 1 March 2027 to 27 May 2027 is 12 weeks and 3 days (87 days).
Source: Wikipedia – Gregorianischer Kalender (Monatslängen, Schaltjahresregel). Updated: .
How it is calculated
A week calculator divides the number of days between two dates by 7: the whole-number part is the full weeks and the remainder is the extra days. In the other direction, every week added to a date is exactly 7 days. The calculation uses the Gregorian calendar and takes leap years into account.
Weeks between two dates
First the days are counted, then divided. Example: from 1 March 2027 to 27 May 2027 there are 30 days in March, 30 in April and 27 in May, 87 days in all. 87 ÷ 7 = 12, remainder 3 – so 12 weeks and 3 days, or 12.43 weeks as a decimal. The start day is not counted, the end day is.
Date plus or minus weeks
12 weeks after 1 March 2027 is 12 × 7 = 84 days later: Monday, 24 May 2027. Six weeks before it is 18 January 2027. Because only whole weeks are added, the weekday stays the same – 1 March 2027 is a Monday too.
- A common year has 365 days, which is 52 weeks and 1 day; a leap year has 52 weeks and 2 days.
- For deadlines given in weeks (“in 6 weeks”), use the second mode: enter the start date and add the weeks.
- The numbered calendar week of a date is something different from a distance in weeks; there is a separate page for that.
Frequently asked questions
How do you calculate the weeks between two dates?
Count the days between the dates and divide by 7. For 87 days that is 12 full weeks and 3 days, or 12.43 weeks as a decimal.
How many weeks are in a year?
52 weeks and 1 day, or 52 weeks and 2 days in a leap year. That is why a fixed date moves on by one weekday each year, and by two after a leap day.
What date is 12 weeks from today?
The start date plus 84 days. Starting from 1 March 2027 that is Monday, 24 May 2027 – the same weekday as the start date.
Is the first day counted?
No. The calculator counts the days from the start date to the end date; from the 1st to the 8th of a month is exactly one week. If the start day should count as well, add one day.
Sources and legal basis
- Wikipedia – Gregorianischer Kalender (Monatslängen, Schaltjahresregel)
- ISO 8601 – Date and time format (Datumsschreibweise JJJJ-MM-TT, Woche = 7 Tage)
As of: · Editorial policy
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