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Add or Subtract Days From a Date

Add or subtract time from any date. Enter a base date and a number of years, months, weeks or days to get the resulting date and the weekday it lands on.

What date is 90 days from now - or 3 months before a deadline? Enter a base date, choose add or subtract, and set any mix of years, months, weeks and days. The calculator returns the resulting date and the weekday it falls on, handling month lengths and leap years for you.

How to use it

  1. Pick a mode

    Difference between two dates, or add/subtract time from a base date.

  2. Enter the dates or offset

    Dates default to today. For add/subtract, set any mix of years, months, weeks and days and choose add or subtract.

  3. Read the result

    Exact years/months/days + totals and business days (difference); the resulting date + weekday (add/subtract).

  4. Share

    Use Copy link to save or send the exact calculation.

What is it?

A date calculator handles two everyday questions: 'how many days between X and Y?' and 'what's the date N days from now?'. Calendar arithmetic looks simple but breaks for month boundaries and leap years; using ISO-8601 rules avoids the surprises.

When to use it

Project deadlines, invoice ageing, contract renewal dates, gestational dates, sprint countdowns, anniversaries, weekday lookup for past events ('what day was 14 March 1987?').

Common mistakes

Treating months as 30 days each - they aren't. Counting business days without subtracting public holidays. Mixing UTC and local time when crossing midnight - the calculator uses UTC to stay stable across timezones.

FAQ

How do I find the number of days between two dates?
Use the difference mode: pick a start and end date and we show the gap in days, weeks, months and years, plus business days, and the exact years/months/days breakdown. The weekday of each date is shown too.
Does it count business (working) days?
Yes. Business days exclude Saturdays and Sundays. Public holidays are not subtracted - they vary by country and region - so deduct any national holidays manually if you need a precise working-day count.
Can I add years and months, not just days?
Yes. In add/subtract mode you can combine years, months, weeks and days in one go, and switch between adding and subtracting. Month lengths and leap years are handled for you (e.g. Jan 31 + 1 month lands in February).
Should I include the end date in the count?
It depends on what you're counting. Exclusive counting (the default) gives the gap between the dates - Monday to Friday is 4 days. Tick 'include end date' for inclusive counting, which counts both endpoints - Monday to Friday becomes 5 days.
What weekday was (or will be) a given date?
The difference mode shows the weekday of both the start and end date, and the add/subtract mode shows the weekday of the resulting date - so you can answer 'what day was 14 March 1987?' or 'what day is 90 days from now?'.
How are months and leap years handled?
Calendar months aren't treated as a flat 30 days, and leap years are respected. All arithmetic runs in UTC so a calculation stays stable even when you cross midnight in your local timezone.

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Date Calculator

Days between dates, add or subtract years/months/days, business-day count.

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