How this calculator works
The calculator counts the whole days between the two dates, then divides by 7. The quotient is the number of full weeks and the remainder is the leftover days. It also adds a number of weeks (each worth 7 days) to the start date so you can find a deadline, due date or follow-up date.
Weeks formula
Weeks = ⌊days ÷ 7⌋, remaining days = days mod 7
Date after N weeks = start date + 7 × N days
Worked example
From 1 January 2026 to 31 December 2026 is 364 days, which is exactly 52 weeks 0 days. Adding 12 weeks (84 days) to 1 January 2026 gives Thu, Mar 26, 2026.
How to use this calculator
- Pick a start date and an end date.
- Enter how many weeks to add to the start date (optional).
- Select Calculate to see weeks and days, total days and the new date.
Frequently asked questions
How many weeks are in a year?
A common year has 52 weeks plus 1 day (365 days) and a leap year has 52 weeks plus 2 days (366 days).
Does the calculator include both the start and end dates?
It counts the elapsed days between the dates, so the end date is not counted as an extra day. Add 1 to the day count if you want both dates included.
Can I count weeks of pregnancy?
Use the Due Date Calculator or Pregnancy Calculator, which are built for gestational weeks.
What if the end date is before the start date?
The difference is shown as a positive number and the result notes that the dates are reversed.
Date arithmetic uses the Gregorian calendar in UTC, so daylight-saving changes do not affect the day count.
Related searches: weeks calculator, week calculator, calculate weeks, online week calculator, weeks calculator online.
Maintained by the CalculatorsOnline Editorial Team. Read our methodology policy.