How many days from 15 March to 10 October? How long did a project take? How many days is a visa valid? These questions all ask for the days between two dates. Counting on a calendar is slow and easy to get wrong. This guide explains how to calculate the difference correctly, and how our free Date Difference Calculator gives days, weeks, months and years in one go.
The basic method
- Count the days left in the start month.
- Add the full days of every month in between.
- Add the days in the end month up to the end date.
Example
From 15 March 2026 to 10 October 2026:
| Part | Days |
|---|---|
| 16–31 March | 16 |
| April to September | 30 + 31 + 30 + 31 + 31 + 30 = 183 |
| 1–10 October | 10 |
| Total | 209 days |
That is 29 weeks and 6 days, or 6 months and 25 days.
Including the end date
The result above counts the days between the dates, which is how most people measure duration. If you need to count both the first and last day, such as for a leave application covering 15 March to 10 October inclusive, add one day: 210 days. The calculator has a checkbox for this.
Leap years
Any period containing 29 February has an extra day. The calculator checks this automatically. You can see which years are leap years with the Leap Year Checker.
Months between two dates
Months have different lengths, so “months” is measured in calendar months: from 15 March to 15 September is 6 months, and the remaining days are counted separately. This is the same method used for age; see the Age Calculator.
Working days
For office deadlines, you may need only Monday to Friday. The calculator shows business days between the dates. Public holidays are not removed automatically, so subtract any from Pakistan Public Holidays that fall in the period.
Common uses
- Visa stays and passport validity
- Notice periods and probation
- Loan and rent periods
- Pregnancy and baby milestones
- Project timelines
For questions about the date that is a certain number of days away, see date counting for visas and contracts or use the Date Calculator (Add or Subtract Days).
Frequently asked questions
How do I calculate the number of days between two dates?
Count the remaining days in the first month, add full months, then add days in the last month, or use a date difference calculator.
Should I include the end date?
For durations, usually not; for inclusive periods like leave, add one day.
Does the calculator handle leap years?
Yes, 29 February is counted automatically.