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Date Calculator online

Calculate date differences and add or subtract days from any date

Date Calculator logo
by
CHUNKY
MUNSTER

// Date Difference

to

// Add / Subtract Days

days

How to Use date-calculator

  1. Choose between Add/Subtract days to a date, or Find the difference between two dates.
  2. Enter the start date (and the days/months/years to add, or the end date).
  3. The result shows the calculated date or the duration in multiple units.
  4. Toggle "exclude weekends" to count only working days.

Date arithmetic is surprisingly complex: adding 1 month to January 31 should give February 28 (not March 3); subtracting 30 days from a date crosses month and year boundaries; and calculating working days must account for weekends. This calculator handles all of these correctly using a calendar-aware date engine.

Calendar-Aware Date Math

Adding calendar months respects month-end clamping: January 31 + 1 month = February 28 (or 29 in a leap year), never March 3. Adding years respects leap years: February 29 + 1 year = February 28 in non-leap years. The difference calculator returns results in multiple units: exact days, business days (Mon–Fri), weeks + days, months + days, and years + months + days, so you can use whichever unit is most relevant.

Frequently Asked Questions

What is the difference between 30 days and 1 month?

Adding "1 month" respects the calendar — January 15 + 1 month = February 15. Adding "30 days" to January 15 = February 14. The difference matters for SLA calculations, subscription periods, and legal contracts.

How are working days calculated?

Working days count Monday through Friday, excluding Saturday and Sunday. Public holidays are not excluded by default (since they vary by country) — the business day count is purely weekday-based.

Can I calculate someone's date of birth from their age?

Use the Add/Subtract mode: subtract the person's age in years from today's date to get the approximate birth year. For an exact birth date, use the Age Calculator in reverse.

Does it handle dates before 1970 (before the Unix epoch)?

Yes — the calculator uses the proleptic Gregorian calendar and works with any date from 1 AD to 9999. Negative Unix timestamps (before 1970-01-01) are handled correctly.

See also the Days Until calculator, Countdown Timer, and Unix Timestamp Converter.