Weeks Between Dates: 5 Mistakes to Avoid
Counts weeks between two dates. The maths is not complicated, but a handful of errors come up again and again in this and related date & time calculations. Here is what to watch for.
The Gregorian calendar has months of 28 to 31 days and adds a leap day almost every four years, which makes counting days by hand surprisingly error-prone. Converting dates to day numbers and subtracting avoids the problem.
Many Singapore rules are expressed in days: notice periods, leave entitlements, stamp duty deadlines and probation periods. Whether the count includes the start or end date, and whether weekends count, changes the answer.
1. Assuming every month has 30 days
Month lengths vary from 28 to 31 days.
2. Not deciding whether to include the end date
Counting inclusively adds one day.
3. Forgetting public holidays
Working-day counts usually need holidays removed.
4. Mixing date formats
5/10 can mean 5 October or 10 May depending on the convention.
5. Ignoring leap years
29 February changes day counts in leap years.
The correct method
Weeks = days ÷ 7.
For example, with these inputs:
- Start date: 5 Jan 2026
- End date: 5 Oct 2026
the calculator returns:
- Weeks: 39.00 weeks
- Full weeks: 39 weeks
Related calculations
- Working Days Calculator: Counts weekdays between two dates, inclusive.
- Day of the Week Calculator: Tells you which weekday any date falls on.
- Months Between Dates Calculator: Counts complete calendar months between two dates.
- Time Duration Calculator: Calculates hours and minutes between two times, including overnight shifts.
The Weeks Between Dates Calculator applies the formula consistently, so it is a quick way to double-check your own working.
Run your own numbers: Weeks Between Dates Calculator