Date Calculator

How to count the days between two dates

1. Open the Days between dates tab and pick a start and an end date. Today is filled in for you.
2. Read the total number of days, plus the same span as years/months/days, weeks, business days, hours, minutes and seconds.
3. Tick Include end date to count both the first and last day: useful for holidays, rentals and “how many days is this event”.

Example: from January 15 to October 26, 2026 is 284 days, which is 9 months, 11 days, or 40 weeks and 4 days, of which 202 are weekdays.

How to add or subtract days from a date

Switch to Add or subtract, choose a start date, an amount and a unit. Ninety days after October 26, 2026 is Sunday, January 24, 2027. Use it for deadlines, notice periods, due dates, warranty and return windows, or “what was the date 6 months ago”.

How months and leap years are handled

• End of month: adding a month keeps the same day number when it exists, otherwise it uses the last day of the month. January 31 + 1 month = 2026-02-28, not March 3.
• Leap days: February 29, 2024 + 1 year = 2025-02-28.
• Month counting: a month is only counted once the end date reaches the same day number. January 31 to February 28 is 28 days, not one month.
• Time zones don’t matter: dates are compared as calendar days, so daylight-saving changes never add or lose an hour.

Business days

Business days are Monday to Friday. When adding business days, weekends are skipped: one business day after Friday, October 30, 2026 is Monday, November 2, 2026. Between two dates, weekdays are counted from the start date up to, but not including, the end date (or including it if you tick the box). Public holidays differ by country and aren’t subtracted, remove them yourself if your deadline excludes them.

Quick reference: dates after January 1, 2027

How the units behave, starting from Friday, January 1, 2027:

Notice that +6 months and +180 days land on different dates: months follow the calendar, days are exact counts. Contracts and notice periods usually say which one they mean, “30 days” and “one month” are not the same.

Calculating age or time since an event

Put the birth date (or event date) as the start and today as the end. Someone born on May 17, 1990 is 36 years, 5 months, 9 days old on October 26, 2026, 13,311 days, or about 1,902 weeks. The years/months/days figure follows the same rule people use for birthdays: a year isn’t complete until the birthday has passed.

Counting days in a spreadsheet or code

Excel / Google Sheets:  =B1-A1              (days between)
                        =NETWORKDAYS(A1,B1) (weekdays, both ends included)
                        =EDATE(A1,6)        (add 6 months)

JavaScript:  const days = Math.round((Date.UTC(2026,9,26) - Date.UTC(2026,0,15)) / 86400000);
Python:      (date(2026,10,26) - date(2026,1,15)).days