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Date Calculator

Find the date a set number of days, weeks, months or years before or after another date, or count how many days and weekdays lie between two dates.

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How to use the date calculator

  1. Choose Add or subtract to move from one date to another, or Days between dates to count the gap.
  2. Enter the start date. It starts on today.
  3. To add or subtract: pick Add or Subtract, then enter any mix of years, months, weeks and days.
  4. To count days: enter the end date. Tick Include the end date to count both the first and the last day, and Count weekdays only to leave out Saturdays and Sundays.
  5. Read the result date or the day count, with the working and the same gap in weeks, months and hours.

How dates are added and counted

Result = (start date ± years and months) ± (7 × weeks + days) Adding months: same day of the month, k months later; if that day doesn't exist, use the last day of the month Days between = end date − start date (+1 when the end date is included) Weekdays = days in that range that fall Monday to Friday

Years and months are applied first because they don't have a fixed length: a month is 28 to 31 days and a year is 365 or 366. Weeks and days are then added as a plain count of calendar days. When counting between two dates, the start date is counted and the end date is not, unless you tick the box. Leap years are handled by the calendar itself, so February 29 is counted whenever it falls in the range.

Worked example

The calculator opens with today's date and adds 90 days. Taking October 29, 2026 as today:

  • October has 2 days left after the 29th, leaving 88 days to add.
  • November uses 30 more, leaving 58.
  • December uses 31 more, leaving 27.
  • 27 days into January gives Wednesday, January 27, 2027.
  • 64 of the 90 days in between are weekdays (12 full weeks give 60, and the last 6 days add 4 more).

For the count mode, January 1, 2026 to December 25, 2026 is 358 days. With both dates included and only weekdays counted, it's 257 weekdays.

End-of-month handling

Adding a month keeps the day of the month, so March 15 plus one month is April 15. Trouble starts on the 29th, 30th and 31st, because some months are shorter. This calculator moves those dates back to the last day of the target month:

Start Change Result
Jan 31, 2026 + 1 month Feb 28, 2026
Jan 31, 2028 + 1 month Feb 29, 2028 (leap year)
Mar 31, 2026 − 1 month Feb 28, 2026
Aug 31, 2026 + 1 month Sep 30, 2026
Feb 29, 2028 + 1 year Feb 28, 2029

Because of this rule, the order of steps matters. January 30 plus one month is February 28, and one more day gives March 1. Add the day first and you get January 31, then February 28. The calculator always does months first, which is the common convention in spreadsheets and programming libraries. If a contract or deadline counts in days, enter the days instead of months to avoid the question.

Frequently asked questions

What date is 90 days from today?

Leave the start date on today and add 90 days, which is the default. From October 29, 2026 the answer is Wednesday, January 27, 2027. Notice periods, return windows and probation periods are often set in days, so this is one of the most common date questions.

Should I include the end date?

It depends on what you're counting. For "how many days until" or the length of a gap, leave it off: Monday to Friday is 4 days. For a period where both the first and last day count, such as days of leave or a five-day course, tick it: Monday to Friday is then 5 days.

Does the weekday count skip public holidays?

No. It counts Monday to Friday only and doesn't know your local holidays, which vary by country and state. Subtract any holidays that fall on weekdays in your range to get working days.

How many days are there in a year?

A common year has 365 days and a leap year has 366. A year is a leap year if it divides by 4, except century years, which must divide by 400. So 2000 and 2028 are leap years, but 1900 and 2100 are not. For a simple count of days to an event, try the day counter.

Related calculators

  • Day Counter — Count the days or weekdays between two dates, with or without the end date, or count down the days to an event.
  • Age Calculator — Your exact age in years, months and days, with totals in weeks, days and hours and the date of your next birthday.
  • Time Duration Calculator — The exact time between two dates and times, in days, hours and minutes, with totals in every unit.
  • Day of the Week Calculator — The weekday for any date from the year 1 to 9999, worked out step by step with Zeller's congruence and the Doomsday rule.

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