📆 Add or Subtract Days from a Date
By ToolNimba Editorial Team · Updated 2026-06-19
Pick a start date, choose add or subtract, then set an amount and a unit.
This calculator adds days, weeks, months, or years to a date, or subtracts them, and tells you exactly where you land. Pick a start date, choose add or subtract, type an amount, and select a unit. You will see the resulting date and the weekday it falls on straight away, so you can answer questions like what date is 90 days from today, or what was the date 6 weeks ago, without counting on a calendar.
What is the Add or Subtract Days Calculator?
Date arithmetic sounds simple but trips people up because months and years are not all the same length. Adding 30 days is not the same as adding one month, and adding one year to 29 February has no exact match in a non-leap year. This tool handles each unit the way most people expect: days and weeks step forward or back by an exact count, while months and years keep the same day-of-month where possible.
For days and weeks the calculation is a pure count. Adding 10 days moves the calendar forward exactly 10 positions, rolling over the end of a month or year automatically. A week is just 7 days, so adding 2 weeks is the same as adding 14 days. Subtracting works the same way in reverse. Because every day is the same length, there is no ambiguity here.
Months and years are where care is needed. When you add one month the tool keeps the same day number if it exists in the target month. If it does not, for example 31 January plus one month, it clamps to the last valid day, giving 28 or 29 February rather than spilling into March. Adding one year to 29 February in a leap year clamps to 28 February. This last-day clamping matches how banks, contracts, and most calendar apps treat month-end dates, and it avoids the surprising jumps you get from naive arithmetic.
When to use it
- Finding the due date of an invoice or contract that is payable a set number of days after issue, such as net 30 or net 60.
- Working out a project deadline that is a number of weeks or months from the kickoff date.
- Counting back to find a deadline, such as the date 14 days before an event when notice is required.
- Estimating a delivery or expiry date by adding days to an order or manufacturing date.
- Answering everyday questions like what date is 100 days from today, or what was 6 months ago.
How to use the Add or Subtract Days Calculator
- Enter the start date, or click Set start to today to use the current date.
- Choose whether to add or subtract.
- Type the amount you want to add or subtract.
- Select the unit: days, weeks, months, or years.
- Read off the resulting date and the weekday it falls on.
Formula & method
Worked examples
Add 30 days to 19 June 2026 (for example, a net-30 invoice issued today).
- Start date is Friday, 19 June 2026.
- June has 30 days, so 19 June plus 11 days reaches 30 June.
- The remaining 19 days carry into July: 30 June plus 19 days is 19 July.
- Check the weekday of the result.
Result: Result: Sunday, 19 July 2026 (2026-07-19)
Add 1 month to 31 January 2026 (a month-end date).
- Start date is 31 January 2026.
- Target month is February, which has 28 days in 2026 (not a leap year).
- Day 31 does not exist in February, so the result clamps to the last day.
- The result is the final day of February, not a spillover into March.
Result: Result: Saturday, 28 February 2026 (2026-02-28)
Subtract 2 weeks from 3 July 2026.
- Two weeks is 2 × 7 = 14 days.
- Subtracting 14 days from 3 July moves back into June.
- 3 July minus 3 days reaches 30 June, with 11 more days to subtract.
- 30 June minus 11 days reaches 19 June.
Result: Result: Friday, 19 June 2026 (2026-06-19)
Examples of adding and subtracting from a start date of 19 June 2026 (a Friday)
| Operation | Resulting date | Weekday |
|---|---|---|
| Add 10 days | 2026-06-29 | Monday |
| Add 30 days | 2026-07-19 | Sunday |
| Add 90 days | 2026-09-17 | Thursday |
| Add 2 weeks | 2026-07-03 | Friday |
| Add 3 months | 2026-09-19 | Saturday |
| Add 1 year | 2027-06-19 | Saturday |
| Subtract 10 days | 2026-06-09 | Tuesday |
Common day-count shortcuts
| Period | Days |
|---|---|
| 1 week | 7 |
| 2 weeks (fortnight) | 14 |
| 4 weeks | 28 |
| 1 calendar quarter (about) | 91 to 92 |
| Half a year (about) | 182 to 184 |
| 1 common year | 365 |
| 1 leap year | 366 |
Common mistakes to avoid
- Treating 30 days as one month. A month is rarely exactly 30 days. Adding 30 days to 31 January lands in early March, while adding one calendar month lands on the last day of February. Choose the unit that matches what you actually mean.
- Expecting month-end dates to keep the same day number. When the target month is shorter, the day clamps down. 31 March plus one month is 30 April, not 31 April, because April only has 30 days. This is the standard convention but it surprises people who expect a fixed day.
- Forgetting leap years. Adding one year to 29 February gives 28 February in a non-leap year. Day counts also differ: a year is 365 days most of the time but 366 in a leap year, so a 365-day jump can miss the same calendar date.
- Confusing inclusive and exclusive counting. This tool adds or subtracts a number of whole days from the start, so the start date itself is day zero. If a rule counts the start date as day one, you may need one fewer day than you expect.
Glossary
- Start date
- The date you begin from, before any days, weeks, months, or years are added or subtracted.
- Unit
- The kind of step you are taking: days, weeks, months, or years. A week equals 7 days.
- Clamping
- Reducing the day number to the last valid day of a month when the original day does not exist there, such as 31 becoming 28 in February.
- Leap year
- A year with 366 days, including 29 February. It occurs every 4 years, except century years not divisible by 400.
- Weekday
- The named day of the week (Sunday through Saturday) that a given date falls on.
Frequently asked questions
What date is 30 days from today?
Set the start date to today (use the Set start to today button), choose Add, enter 30, and select Days. The tool shows the resulting date and the weekday it lands on. Days roll across month and year boundaries automatically.
How do I subtract days from a date?
Enter the start date, choose Subtract, type the number of days, and keep the unit on Days. The result is the earlier date that many days before your start, with the weekday shown alongside it.
Why does adding one month to 31 January give 28 February?
February does not have a 31st day, so the result is clamped to the last valid day of the target month. This matches how most calendars, banks, and contracts treat month-end dates and avoids spilling into the next month.
Is adding 4 weeks the same as adding one month?
No. Four weeks is exactly 28 days, while a calendar month is 28 to 31 days. They only match in February of a non-leap year. Use the Weeks unit for an exact 28-day step and the Months unit to keep the same day number.
Does the calculator account for leap years?
Yes. Day and week counts step across 29 February correctly, and adding a year to 29 February clamps to 28 February in a non-leap year. The weekday shown always reflects the true calendar, including leap days.
Does the time zone affect the result?
No. Dates are handled as plain calendar dates at local midnight, so there is no time-zone shift. The date you enter and the date you get back are both read as calendar days, not moments in time.