Date Calculator
Add days, weeks or months to a date, or count the gap between two dates.
Date & Time Calculators
Use tool
Add or Subtract Days Calculator
The date a given number of days, weeks, months or years away.
Add or Subtract Days Calculator tool
Month arithmetic clamps to the end of the month: 31 January plus one month is 28 February.
—
Resulting date
—
Day of the week
—
ISO format
—
Calendar days apart
—
ISO week number
| Interval | Resulting date |
|---|
About the Add or Subtract Days Calculator
Add or Subtract Days Calculator answers the 'what date will it be' question for any interval: days, weeks, months, years, or a combination. It works in both directions, and it can count the days as working days only when the interval is a deadline rather than a calendar gap.
Month arithmetic is the part that needs a rule, and the rule here is to clamp to the end of the month. Thirty-one January plus one month is twenty-eight February, not the third of March. That is what almost every legal and accounting convention does, and it is what spreadsheets do, but it means adding a month twice is not always the same as adding two months.
Months are applied before days, which matters when you combine them. The order is stated rather than left to chance, because 'one month and thirty days' can land on two different dates depending on which is applied first.
The page shows its working, not just its answer. Where there is a formula it is printed with your own numbers substituted in, so you can check the result rather than take it on trust -- which is the difference between a calculator you can use for something that matters and one you cannot.
Everything runs inside your browser. What you type is never uploaded, never logged and never stored, and the calculator keeps working if your connection drops after the page has loaded.
Looking for something this does not cover? FreeToolsHub.org is another hub of free online tools that need no account, and it is worth a look if add or subtract days calculator is only part of what you are working on.
How to use the Add or Subtract Days Calculator
- Choose directionThe fields below change to match what you pick, so only the figures that matter to your case are asked for.
- Enter start date, days and weeksDecimals are fine, and thousands separators are accepted and ignored.
- Read the resulting date, day of the week and iso formatThe figures update as you type. The Calculate button is there if you would rather press something, but nothing waits for it.
- Copy or check the resultCopy the summary with the copy button, or open the table to check it row by row.
Features
- Shows resulting date, day of the week, iso format, calendar days apart and iso week number together, so you are not running it twice
- A results table you can read across
- Updates as you type, with no button to press and no page reload
- Copy the result in one click
- Free, no sign-up, and it runs entirely in your browser
Who uses this tool
The add or subtract days calculator is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:
- Finding a date 90 days from today
- Working out a contract end date
- Counting back to a start date from a deadline
- Adding months while respecting month lengths
Frequently asked questions
What happens when the month is too short?
The date clamps to the last day of the month. 31 January plus one month is 28 February, or 29 in a leap year.
Are months applied before days?
Yes. Combining both applies the months first, then the days, which is stated here because the other order can give a different date.
How do I count backwards?
Choose subtract. The interval is applied in reverse and the span is still reported as a positive number of days.
Related tools
If the add or subtract days calculator is not quite what you need, these other free tools solve closely related problems, and there are 13 more in date & time calculators.
Business Days Calculator
Count working days between dates, or add them to one.
Date & Time Calculators
Use tool
Days Until Calculator
Countdown to any date in days, weeks and working days.
Date & Time Calculators
Use tool
Day of the Week Calculator
The weekday for any date, past or future.
Date & Time Calculators
Use tool
Age Calculator
Enter a date of birth to get an exact age plus total months, weeks and days.
Date & Time Calculators
Use tool
Checked and rebuilt on 2026-10-14. The method this calculator uses is described in the section above, and corrections go through the contact page.