Add or subtract days from a date
Pick a start date, then enter the number of days, weeks, months or years to add or subtract. The calculator shows the resulting date with its day of the week, ISO week number and day of the year. Month ends and leap years are handled, so 90 days from today is always exact.
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- 📱 Works on mobile
- ⚡ Instant results
🔒 Everything runs in your browser. Your data and files never leave your device.
📌 Key facts
- Adding days to a date moves forward or backward on the calendar by whole calendar days, ignoring time of day.
- One year is 12 months and one week is 7 days; the calculator applies years and months before weeks and days.
- One month after January 31 lands on February 28 (February 29 in a leap year) because the last day of the month is used.
- Adding 30 days is not the same as adding 1 month: 30 days after January 31, 2026 is March 2, 2026.
- 45 days after October 30, 2026 is December 14, 2026.
- Weekends and holidays are not skipped when you add calendar days.
In what order the calculator adds
Years and months are applied first, then weeks and days. One year is 12 months and one week is 7 days.
\[ \text{result} = (\text{start} \pm \text{months}) \pm (7 \times \text{weeks} + \text{days}) \]
If the start day does not exist in the target month, the last day of that month is used. The math uses calendar dates, so daylight saving time never shifts the answer.
Month ends and February 29
| Start | Operation | Result |
|---|---|---|
| 01/31/2026 | + 1 month | 02/28/2026 |
| 03/31/2026 | − 1 month | 02/28/2026 |
| 02/29/2024 | + 1 year | 02/28/2025 |
| 05/31/2026 | + 4 months | 09/30/2026 |
Adding 30 days is not the same as adding 1 month: 30 days from 01/31/2026 lands on 03/02/2026.
Common deadlines
| Deadline | How to calculate |
|---|---|
| 14-day return window | + 14 days (calendar days) |
| 90-day trial or probation | + 90 days |
| 2 months notice | + 2 months |
| 2-year warranty | + 2 years |
For a deadline in business days, use the business days calculator.
Add days to a date: a step-by-step method
Here is how to get a reliable answer. First, enter your start date. Then pick add or subtract. Next, fill in years, months, weeks and days. Finally, read the result and its day of the week.
- Choose the start date, for example October 30, 2026.
- Enter the amount: 45 days, 6 weeks or 3 months.
- Check the direction: add for a deadline, subtract for a past date.
- Copy the result and its ISO week number into your calendar.
For example, 45 days after October 30, 2026 is December 14, 2026. That is because October 30 to November 30 spans 31 days, so 14 days remain in December. If the span is long, split it into months and then days. That way you can check each step.
Add days to a date: common mistakes
A few traps come up again and again. First, people mix calendar days and business days. A 10 business day deadline is not 10 days, so use the business days calculator instead. Second, months have different lengths, so one month is not always 30 days.
- Counting the start day: most deadlines exclude it, but check your contract.
- Treating 1 month and 30 days as the same thing.
- Forgetting holidays, because some legal deadlines roll to the next business day.
When you only need the gap between two known dates, try the days between dates calculator. To place a date in the year, open the week number tool. Also check the federal holidays calendar before you set a due date.
Common deadlines you can add days to a date for
These are the periods people calculate most. So you save time when a due date is close.
| Situation | Typical length | Counting |
|---|---|---|
| Return window at many stores | 30 days | Calendar days |
| Probation or trial period | 90 days | Calendar days |
| Notice to a landlord | 30 to 60 days | Calendar days |
| Credit card billing cycle | About 30 days | Calendar days |
However, every contract can set its own rule. Therefore, read the clause before you commit to a date.
3 real-life examples
90 days from October 30, 2026
October 30, \( 2026 + 90 \) days = Thursday, January 28, 2027, ISO week 4 of 2027, the 28th day of the year.
One month after January 31
January 31, \( 2026 + 1 \) month = Saturday, February 28, 2026. February has no 31st, so the last day of the month is used. In a leap year such as 2024 the answer would be February 29.
6 weeks from today, and 45 days ago
October 30, \( 2026 + 6 \) weeks = Friday, December 11, 2026. Switch to "Subtract" and 45 days before October 30, 2026 is Tuesday, September 15, 2026.