Add or Subtract Days Calculator
Add or subtract days, weeks, months or years from any start date and instantly see the resulting date with its weekday. Free, fast and fully private.
What is the Add or Subtract Days Calculator?
The ByteTools Add or Subtract Days Calculator does calendar arithmetic for you: pick a start date, choose to add or subtract, and enter any mix of days, weeks, months and years.
- Add or subtract days, weeks, months and years together
- Shows the resulting date plus its day of the week
- Correct month-end handling (Jan 31 + 1 month = Feb 28/29)
- Handles leap years automatically
- One-click Today button for quick calculations
- 100% private — dates never leave your browser
How to use the Add or Subtract Days Calculator
- 1
Pick your start date (or click Today).
- 2
Choose whether to add or subtract time.
- 3
Enter the number of days, weeks, months and/or years to shift by.
- 4
Read the resulting date and its weekday instantly.
About the Add or Subtract Days Calculator
The ByteTools Add or Subtract Days Calculator does calendar arithmetic for you: pick a start date, choose to add or subtract, and enter any mix of days, weeks, months and years. It instantly returns the resulting date along with the exact day of the week, so you never have to count on a calendar again.
It is perfect for working out deadlines, warranty expiry dates, contract end dates, appointment reminders, medication schedules and "90 days from now" style questions. Month and year jumps use real calendar lengths, so adding one month to January 31 lands correctly on the last day of February rather than overflowing.
Every calculation runs entirely in your browser with JavaScript — no dates are uploaded to any server, so it is safe for confidential legal, medical or financial planning.
Frequently asked questions
How do I calculate a date 90 days from today?
Click Today to set the start date, choose Add, and type 90 into the days field. The calculator immediately shows the exact date 90 days later along with the weekday it falls on.
What happens when I add a month to the 31st?
Adding one month to a date like January 31 lands on the last valid day of the next month — February 28 (or 29 in a leap year) — because that month has no 31st. This matches how banks and contracts usually treat month-end dates.
Can I subtract days to find a past date?
Yes. Choose Subtract and enter the number of days, weeks, months or years, and the tool counts backwards from your start date to show the earlier date and its day of the week.
Does the calculator handle leap years?
Yes. It uses the JavaScript Date engine, which follows the Gregorian calendar, so February 29 in leap years such as 2028 is counted automatically when you add or subtract days across it.
Do weeks and months add up together?
Yes. You can combine fields — for example add 2 weeks and 3 days at once. Years and months are applied first as calendar jumps, then weeks and days are added as fixed 7-day and 1-day steps.
Guides for Add or Subtract Days Calculator
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