Date Difference Calculator
This free date difference calculator counts the time between two dates in days, weeks, months and years, and also gives the exact difference in years, months and days plus an estimate of business days. It is useful for deadlines, contracts, trips, pregnancies, projects and countdowns.
How to use the date difference calculator
- Pick the start date.
- Pick the end date. If you enter them in the wrong order the calculator swaps them for you.
- Press Calculate Difference to see the totals and the exact breakdown.
How the difference between two dates is calculated
The total number of days is the real calendar distance between the two dates, so leap years (366 days) and months of 28, 29, 30 or 31 days are all taken into account. From that total the calculator derives:
- Weeks: total days ÷ 7, rounded down.
- Months and years: totals based on the average month (30.44 days) and year (365.25 days).
- Exact difference: full years, then full months, then the remaining days, counted on the calendar the way you would by hand.
- Business days (approximate): total days × 5 ÷ 7. Public holidays are not removed because they change from country to country.
Worked example
From 1 March 2026 to 25 December 2026 there are 299 days, which is 42 weeks and 5 days. The exact calendar difference is 9 months and 24 days, and there are about 214 weekdays (Monday to Friday) in between.
Should the start or end date be counted?
Like most date tools, this calculator counts the days between the dates: from 1 March to 2 March is 1 day. If you need to include both the first and the last day, for example to count the days of a hotel stay or a work contract, add 1 to the total.
Common uses
- Counting down to a birthday, holiday, exam or wedding.
- Working out how many days are left on a lease, warranty, subscription or visa.
- Calculating notice periods, invoice terms (for example “net 30”) and payment delays.
- Measuring how long a project, trip or job lasted.
- Planning milestones, such as 100 days from a start date.
Frequently asked questions about the date difference calculator
Does the date difference calculator include the end date?
No, it counts the days between the dates. Add one day if you want to include both the start and the end date.
How are business days calculated?
They are estimated as five sevenths of the total days. Weekends are excluded on average; holidays are not, because they depend on your country.
Can I use dates in the past?
Yes, any two dates work, past or future.
Does it account for leap years?
Yes. Every 29 February between the two dates is counted.
Why do the total months and the exact months differ slightly?
The totals use an average month length, while the exact breakdown follows the real calendar. For precise answers, use the exact years, months and days line.
How many days are in each month?
| Month | Days |
|---|---|
| January | 31 |
| February | 28 (29 in leap years) |
| March | 31 |
| April | 30 |
| May | 31 |
| June | 30 |
| July | 31 |
| August | 31 |
| September | 30 |
| October | 31 |
| November | 30 |
| December | 31 |
A year has 365 days, or 366 in a leap year. Leap years are years divisible by 4, except century years that are not divisible by 400: 2024 and 2028 are leap years, 1900 was not, and 2000 was. This is why counting months by hand often goes wrong, and why a date difference calculator saves time.
Tips for counting deadlines
- Check whether a contract counts calendar days or business days; the result can differ by weeks.
- For “30 days from today”, add 30 to the start date rather than “one month”, since months have different lengths.
- Write the result as a date, not only as a number of days, to avoid confusion later.
Related tools
- Age Calculator – the same calendar logic applied to a date of birth.
- Time Duration Calculator – for differences in hours and minutes within a day.
- Loan Repayment Calculator – plan payments over a number of months or years.
- All free tools
Further reading: Julian day, the system astronomers use to count days between dates.