Date Calculator
Count the days between two dates, or add and subtract time from a date.
Work out exactly how many days, weeks, months, or years fall between two dates, or start from one date and add or subtract a span of time to land on another — both directions people constantly need for deadlines, contracts, and travel planning.
Leap years and varying month lengths are handled automatically, so the count is exact rather than a rough estimate.
Inclusive or exclusive counting
This is the question that causes most date-arithmetic disputes. From Monday to Wednesday is two days if you count the gaps, and three if you count the days themselves. Contracts, notice periods and hotel bookings each use different conventions, and a difference of one day can matter a great deal.
- Hotel nights, rental periods and interest accrual are usually exclusive — you count the gaps, so Monday to Wednesday is 2.
- Event durations and leave applications are usually inclusive — a conference running Monday to Wednesday lasts 3 days.
- Legal notice periods vary by jurisdiction and often exclude the first day but include the last. Check the wording rather than assuming.
- This calculator counts exclusively by default, matching most calendar and scheduling software.
Month arithmetic and end-of-month edge cases
| Starting date | Add one month | Why |
|---|---|---|
| 15 January | 15 February | Straightforward — the day exists. |
| 31 January | 28 February (29 in a leap year) | 31 February doesn't exist, so it clamps to the last valid day. |
| 31 March | 30 April | Same clamping rule. |
| 28 February | 28 March | Clamping only applies when the target day is invalid. |
Adding one month then subtracting one month is not always the identity operation: 31 January → 28 February → 28 January.
Frequently asked questions
- Does this count the start and end date as one day or two?
- The date difference is exclusive by default — from Monday to Wednesday is 2 days — matching how most calendar and scheduling tools count.
- Can I subtract months from a date, not just add them?
- Yes, enter a negative value (or use the subtract mode) to move backward from a starting date.
- How are months counted when day counts differ?
- Adding one month to January 31st lands on the last valid day of February, following the same convention most calendar apps use.
- Can I count only working days?
- The main count includes every calendar day. To approximate working days, divide the total by 7 and multiply by 5, then adjust manually for public holidays in your region.
- Why is adding 12 months not always the same as adding 365 days?
- A leap year contains 366 days. Adding 12 months from 1 March 2027 gives 1 March 2028, but adding 365 days gives 29 February 2028.