Add or subtract time from a date
Choose a start date and how much to add or subtract and see the resulting date and its weekday.
Free · no signup Runs in your browser
How do I add days to a date?
Choose the start date (leave it empty for today), choose Add or Subtract, and type how many years, months, weeks and days. The calculator shows the resulting date with its weekday. Months are added with the month end kept inside the month, so 31 January plus one month is the last day of February, and weeks and days are added after that.
Dates that move by months and by days
Adding days is easy: a day is a day. Adding months is not, because months have different lengths. Adding one month to 31 January has no 31 February to land on, so the sensible answer is the last day of February. This calculator uses that rule and applies years and months first, then weeks and days, which is the order most contracts, leases and notices read.
Common uses are deadlines (30 days from receipt, 90 days from a notice), due dates, warranty and return windows, and project plans. The result shows the weekday so you can see at once if it falls on a weekend, which often matters for a deadline. It does not skip weekends or holidays; for working days use the business days calculator. Enter zero in any box you do not need.
It runs in your browser. The dates you enter are never sent anywhere.
How it works
You choose a start date (empty means today), choose Add or Subtract and enter years, months, weeks and days. The calculator adds the years and months first, keeping the same day of the month, or the last day of the new month if that month is shorter: January 31, 2026 plus one month is February 28, 2026. Then it adds weeks × 7 plus the days. The result is shown with its weekday. Subtracting follows the same steps with negative amounts. The calculation uses calendar dates in UTC, so daylight saving time cannot move the result by a day. The month-end rule is the common one but not the only one: some contracts count one month from 31 January as 28 February, others as 3 March, so check the wording of your document.
How to use it
- Choose the start date, or leave it empty for today.
- Choose Add or Subtract.
- Enter the years, months, weeks and days (any of them can be zero).
- Read the resulting date and its weekday.
- To count business days instead of calendar days, use the business days calculator.
What the calculation assumes
What goes into the answer, and what does not.
| Aspect | What happens |
|---|---|
| Calendar days | Counted, including weekends and holidays |
| Month ends | Kept inside the month: 31 January + 1 month = 28 February |
| Daylight saving | No effect, because dates are used, not times |
| Order of the steps | Years and months first, then weeks and days |
| Business days | Not skipped: weekends and holidays are counted |
| Privacy | Everything is worked out in your browser; nothing you enter is uploaded or saved |
When to use it
- Finding a deadline 30, 60 or 90 days away
- Working out the end date of a lease, warranty or trial
- Counting forward weeks or months in a plan
- Finding the date a number of days ago
Problems you may run into
Most differences come from the inputs and from the meaning of the numbers.
| What you see | Likely cause | What to do |
|---|---|---|
| The date lands on the 28th instead of the 31st | The next month is shorter | That is the month-end rule; check your document if it counts differently |
| I need working days | This counts calendar days | Use the business days calculator |
| Different from my contract | Contracts can define a month in their own way | Follow the wording of the contract or ask a lawyer |
| Leap years | 29 February exists only in leap years | The calculator handles leap years; 29 February plus one year is 28 February |
| Negative numbers | Use Subtract instead | Choose Subtract and enter positive numbers |
Mistakes it helps you avoid
- Adding 30 days when the rule says one month.
- Forgetting that a deadline may fall on a weekend or holiday.
- Assuming every month has 30 days.
- Mixing up adding and subtracting.
The formula
How the answer is worked out.
add years and months first: the same day-of-month in the new month, or the last day of that month if it is shorterthen add weeks × 7 + daysweekday = the day of the week of the resulting datesubtract = the same steps with negative amounts
The calculation uses calendar dates in UTC, so it is unaffected by daylight saving time. The month-end rule is the common one but not the only one: some contracts count 'one month' from 31 January as 28 February, others as 3 March, so check the wording of your document.
Example: 90 days and 1 month from January 31, 2026
You add 1 month and then 90 days to January 31, 2026.
- Add 1 monthFebruary 28, 2026 (the month end is clamped)
- Add 90 daysMay 29, 2026
Friday, May 29, 2026
Adding the 90 days first and the month second would give a different date.
Terms on this page
- Month-end rule
- When adding months lands on a day that does not exist, the last day of the month is used.
- Calendar days
- Every day, including weekends and holidays.
Common questions
What is 90 days from today?
Leave the start date empty, enter 90 in the Days box and read the date.
What happens when I add a month to the 31st?
The result is the last day of the shorter month, for example 28 or 29 February.
Can I subtract time?
Yes. Choose Subtract.
Is anything I enter sent to a server?
No. The calculation happens in your browser and nothing you type leaves your device.
Does it skip weekends?
No. It counts every calendar day. Use the business days calculator for working days.
Where these numbers come from
- Wikipedia — Gregorian calendar The leap-year rule and month lengths used in the calculation.
- W3C — Date and Time Formats (ISO 8601 profile) The YYYY-MM-DD form used for dates.
- MDN Web Docs — Date.UTC() How a browser counts calendar days without daylight-saving shifts.
Last verified 2026-10-25 The method on this page is checked against the sources above at least once a year. Spotted something out of date? Tell us and we will fix it.
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