Date Calculator (Days Between Dates)

Count the days from one date to another

Ask someone how many days are left until a deadline and they will usually grab a calendar and start counting squares. That works, but it is slow, and it is easy to lose your place at the end of a month. This calculator does the counting for you. Put in two dates and it gives you the gap in days, in weeks, and in years, months and days, plus how many of those days fall on a weekday.

It also works the other way round. Start from a date, add or take away some years, months, weeks or days, and it shows the date you land on. That is handy for notice periods, project deadlines, visa stays, or finding the date 90 days from today.

How to use it

1. Choose Days between dates to count a gap, or Add or subtract time to find a new date.
2. For a gap, pick the start date and the end date. You can type them or use the date picker.
3. Tick Count the end date too if both days should be in the count, like a week of leave from Monday to Friday.
4. For a new date, pick the start date, choose Add or Subtract, then fill in years, months, weeks and days. Leave any box you do not need at 0.
5. Read the answer next to the form, or just below it on a phone. Copy result copies the answer, and Copy link gives you a link with your dates already filled in.

The formula behind it

Counting days between two dates is a subtraction. Each date is turned into a day number, which is the count of days since a fixed starting point, and the earlier number is taken from the later one.

days between = end date − start date
days with both ends counted = end date − start date + 1
weeks = days ÷ 7, and the remainder is the extra days

Turning dates into day numbers is what keeps the maths honest. It takes care of months with 28, 29, 30 or 31 days and of leap years, so there are no special rules for you to remember. Weekdays are counted by going through the range and leaving out every Saturday and Sunday.

Adding months is the one place where a choice has to be made. One month after 31 January cannot be 31 February, so the calculator uses the last day of the month instead: 31 January 2026 plus one month is 28 February 2026. Years and months are added first, then weeks and days.

Worked example: 1 January to 15 March 2026

Say a project starts on 1 January 2026 and the client wants it finished by 15 March 2026. How many days is that? Split it at the start of each month:

• 1 January to 1 February: 31 days
• 1 February to 1 March: 28 days, because 2026 is not a leap year
• 1 March to 15 March: 14 days

Add them up and you get 73 days. That is 10 weeks and 3 days, or 2 months, 14 days. Of those 73 days, 52 are weekdays and 21 fall on a weekend. Tick Count the end date too and the answer becomes 74 days, because 15 March itself now counts.

Reading the answer

The main number is in calendar days. That is what most contracts, notice periods and countdowns mean when they simply say "days". If yours says working days or business days, use the weekday count instead, and keep in mind that it does not know about public holidays. The business days calculator lets you take holidays out as well.

The years, months and days line is useful for an age or a length of service. Months are not all the same length, so 2 months, 14 days describes the gap in calendar terms rather than standing for a fixed number of days.

Mistakes that throw the count off

• Forgetting whether the end date counts. Monday to Friday is 4 days by subtraction, but 5 days if you mean both Monday and Friday. Decide which one your situation needs before you rely on the number.
• Treating every month as 30 days. Three months from 1 July ends on 1 October, which is 92 days, not the 90 you get from 3 times 30.
• Mixing up date formats. 03/04/2026 is 3 April in the UK and March 4 in the US. The date picker avoids this, so use it when a date looks ambiguous.
• Leaving out leap years. February has 29 days in 2028, so any range that crosses it is one day longer than the same range in 2027.

Days in each month

A leap year is any year divisible by 4, except century years that are not divisible by 400. So 2000 was a leap year, 2028 will be one, and 2100 will not.

Frequently asked questions

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• Weeks, Months and Years CalculatorWeeks, months and years between two dates, converting between them, and the week number of any date.

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