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Calculate · Calendar dates

Date Calculator

Add or subtract years, months, and days from a calendar date and see the resulting date and day of the week.

Add or subtract

Calculate a new date

Runs in your browser
Operation
Resulting dateSeptember 10, 2026

Thursday

The calculation uses calendar dates, not elapsed 24-hour periods or time zones.

Add or subtract time from a date

Choose a start date, select whether to add or subtract, and enter whole numbers of years, months, and days. The calculator applies the values in that order: years first, then months, then days.

Applying units in a fixed order matters near the end of a month. For example, adding one month and one day to January 31, 2025 produces March 1, 2025: one month first reaches February 28, then one day reaches March 1.

How month-end dates are handled

If the target month has fewer days than the start month, the result uses the last valid day of the target month. Examples:

  • January 31 plus one month becomes February 28 in 2025.
  • January 31 plus one month becomes February 29 in leap year 2024.
  • February 29, 2024 plus one year becomes February 28, 2025.

This “clamp to month end” rule makes every calculation produce a valid calendar date. Other systems may use rollover rules, so check the convention required for financial contracts or recurring billing.

Calendar days versus weekdays

By default, the days field counts every calendar day. Enable business-day mode to count Monday through Friday while skipping weekends. Public holidays are never excluded because holiday calendars differ by country and region, so the result is not automatically an official business deadline.

Example calculations

Project deadline

Adding 45 days to April 10, 2025 results in May 25, 2025. Weekends are included.

Date one year earlier

Subtracting one year from October 7, 2025 results in October 7, 2024.

Subscription month

Adding one month to August 31, 2025 results in September 30, 2025 because September has only 30 days.

Accuracy and limitations

Inputs are treated as dates without a time or time zone. This is appropriate for birthdays, calendar planning, and ordinary date arithmetic. It is not an elapsed-hours calculator and does not account for daylight-saving transitions, leap seconds, working hours, or jurisdiction-specific deadline rules.

Use Days Between Dates to measure an existing interval, or Age Calculator for a birth-date-oriented result.