How to use this date calculator
- Days between dates: pick a start and an end date (or press Today). You’ll see the total days, the same span in weeks, months and years, the number of business days, and the hours and minutes. Tick Include end day to count both dates, and add your own holidays to leave them out of the business-day count.
- Add or subtract: pick a start date, choose Add or Subtract, and enter any mix of years, months, weeks and days. Tick Count business days only to skip weekends and your holidays when counting the days.
- Days until / day of week: choose a date, or press a holiday to jump to its next occurrence, to see how many days are left (or have passed) and which day of the week it falls on.
Everything works on whole calendar days, so clock changes for daylight saving can’t throw a result off by a day. Nothing you enter is saved.
How to count the days between two dates
The number of days between two dates is the later date minus the earlier one. From 1 January 2026 to 31 December 2026 is 364 days. That count includes the start day but not the end day, the same way a hotel counts nights: arriving on the 1st and leaving on the 2nd is one night.
Sometimes you want to count both days, for example a conference that runs from the 1st to the 3rd lasts three days, not two. That’s what Include end day (+1) does: 1 January to 31 December becomes 365 days. If the end date is before the start date, the result is shown as negative, meaning the end date is in the past relative to the start.
Business days vs calendar days
Calendar days are every day, weekends included. Business days (or working days) are Monday to Friday only. March 2026, counted from the 1st to the 31st inclusive, has 31 calendar days but only 22 business days. Public holidays vary by country, region and employer, so this calculator doesn’t guess them: add the dates you take off and they’ll be skipped. Business days are useful for delivery times, notice periods and project deadlines, where weekends don’t count.
Adding months and years: month-end and leap-year rules
Days and weeks are easy to add, but months and years are trickier because months have different lengths. Adding a month keeps the same day number, unless the new month is too short, in which case the date moves to the last day of that month:
- 31 January 2026 + 1 month = 28 February 2026 (February 2026 has only 28 days).
- 31 January 2024 + 1 month = 29 February 2024 (a leap year).
- 29 February 2024 + 1 year = 28 February 2025, because 2025 has no 29 February.
The calculator adds years and months first, then weeks and days, and shows a note whenever a date has been moved to the end of a month.
Leap years explained
A year has about 365.2425 days, so the calendar adds a 29 February to stay in step with the seasons. The rule is: a year is a leap year if it divides by 4, except for century years (those ending in 00), which are leap years only if they also divide by 400. So 2024 is a leap year, 2026 is not, 2000 was (it divides by 400), and 1900 and 2100 are not. A leap year has 366 days, which is why 1 January 2024 to 1 January 2025 is 366 days, or 52 weeks and 2 days.
How to find the day of the week for any date
The days of the week repeat every 7 days, so if you know the weekday of one date, you can find any other by counting the days between them and looking at the remainder after dividing by 7. For example, 22 October 2026 is a Thursday. Christmas Day is 64 days later, and 64 = 9 × 7 + 1, so 25 December 2026 is one day after a Thursday: a Friday. The calculator does this for every date you enter.
Frequently asked questions
How many days are there between two dates?
Subtract the earlier date from the later one, counting whole days. From 1 January 2026 to 31 December 2026 is 364 days. If you want to count both the first and the last day, add one: 365 days.
What does “include end day” mean?
Normally the count includes the start day but not the end day, like counting nights in a hotel. Ticking “Include end day” adds one so both dates are counted, which is what you want for things like the length of an event that runs from one date to another inclusive.
How are business days counted?
Business days are Monday to Friday. Saturdays and Sundays are skipped, and so are any holidays you add yourself. The calculator doesn’t include built-in public holidays, because they differ from place to place.
What is 31 January plus one month?
February has no 31st, so the date moves to the last day of February: 28 February, or 29 February in a leap year. The calculator always does this when a month is shorter, and shows a note when it happens.
Is 2000 a leap year? Is 1900?
A year is a leap year if it divides by 4, except for century years, which must also divide by 400. So 2000 was a leap year, but 1900 was not, and 2100 won’t be.
How many days until Christmas?
Open the “Days until” tab and press Christmas: the calculator picks the next 25 December and counts the days from today, along with the day of the week it falls on. The same works for New Year’s Day, Valentine’s Day, Halloween or any date you choose.