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Date & Time calculator

Date Calculator

Add or subtract days, weeks, months, or years from a calendar date, including month-end and leap-year clamping.

Result date2026-07-27

Dates are UTC calendar dates. Adding one month to January 31 lands on February 28 or 29, not March 2 or 3.

FormulaResult date = start date ± N calendar days, weeks, months, or years
Calculation steps
  1. Add 26 days to 2026-07-01.
  2. Months and years keep the day of month when it exists; otherwise they clamp to the last day of the target month.
  3. Result = 2026-07-27

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How it works

How to use this date calculator

  1. Choose Add or Subtract.
  2. Enter the start date, a non-negative whole amount, and the unit.
  3. Read the result date on the UTC calendar.

Formula

The calculation formula

Result date = start date ± N calendar days, weeks, months, or years
01

Read the start date as a UTC calendar date.

02

Add or subtract whole days or weeks as 24-hour calendar steps.

03

For months and years, keep the day of month when it exists; otherwise use the last day of the target month.

Worked examples

Example calculations

Add days

2026-07-01 + 26 days = 2026-07-27, the same pair used by Date Difference as 26 elapsed days.

Leap day and month end

2024-02-29 + 1 year = 2025-02-28. 2026-01-31 + 1 month = 2026-02-28, not 2 or 3 March.

When to use it

Common use cases

  • Find the date 26 days after a start date
  • Move back two weeks
  • See where 31 January plus one month lands in a common year

Limits

Assumptions and limits

  • Dates are UTC calendar dates, not local midnights, so daylight-saving does not shift the day.
  • The amount is unsigned. Use Subtract to move earlier.
  • Invalid calendar dates such as 31 February are rejected.
  • This page answers “what date is N units away.” Use Date Difference to count the span between two known dates.

Questions

Frequently asked questions

What happens if I add a month to 31 January?

The result is the last day of February: 28 February in 2026, or 29 February in a leap year. The extra days are not spilled into March.

How is this different from Date Difference?

Date Difference starts with two dates and returns a count. Date Calculator starts with one date and an offset and returns the other date.

Sources

Sources and review