How to count the days between two dates

The calculator starts at today and Christmas Day. Change either date and the numbers update straight away.

If you just needed the number, you’re done. If you want to know how to work it out yourself, or in a spreadsheet, or why your answer is one off from somebody else’s, read on.

The one-day difference, explained

This catches everyone out at some point, so it’s worth getting out of the way first.

Say you’re checking into a hotel on Friday and leaving on Sunday. That’s 2 nights. But if you’re going to a festival that runs Friday to Sunday, that’s 3 days. Same dates, different answers, and both are right.

• Days between counts the gaps. From Friday to Sunday is 2. This is what most calculators, spreadsheets and countdown apps give you.
• Counting both days counts the days themselves. Friday, Saturday, Sunday is 3. It’s always one more.

A countdown uses the first one. If it’s Friday and your trip is on Sunday, you’ve got 2 days to go. Use the second one for things like holiday leave or how many days a course runs.

Counting by hand

You don’t need a calculator for most of these. The trick is to split it into three pieces: what’s left of the first month, the full months in the middle, and the days into the last month.

From 22 October to 25 December:

• Rest of October: 31 − 22 = 9
• All of November: 30
• Into December: 25

9 + 30 + 25 = 64 days.

You do need to know how long each month is. The rhyme works (“Thirty days hath September, April, June and November…”), and so does the knuckle trick: make a fist, and count the months across your knuckles and the gaps between them. Knuckles are 31 days, gaps are 30, except February. July lands on the last knuckle, so start again from the first one for August.

Leap years

February has 29 days in a leap year. A year is a leap year if it divides by 4, unless it divides by 100, in which case it isn’t, unless it also divides by 400. So 2028 is a leap year, 2100 won’t be, and 2000 was. 2026 and 2027 are normal years.

In Excel

Excel stores dates as numbers (days since the start of 1900), so you can just subtract them. With the start date in A2 and the end date in B2:

A few things that trip people up:

• DAYS takes the end date first. =DAYS(A2,B2) gives you a negative number.
• If the answer looks like a date (something in early 1900), the cell is formatted as a date. Change it to Number or General.
• NETWORKDAYS includes both ends. Monday to Friday of one week gives 5, not 4.
• If your weekend isn’t Saturday and Sunday, use NETWORKDAYS.INTL, which lets you choose which days count as the weekend.
• Avoid DATEDIF with "md". Microsoft’s own documentation warns it can give wrong results. The "d", "m" and "y" options are fine.

In Google Sheets

Good news: it’s the same. =B2-A2, =DAYS(B2,A2), =NETWORKDAYS(A2,B2) and =DATEDIF(A2,B2,"d") all work in Google Sheets exactly as they do in Excel. =TODAY() updates each time the sheet recalculates, so a “days until” column keeps itself current.

If you’re writing code

The classic mistake is to subtract two timestamps and divide by 86,400,000 (milliseconds in a day). It works until a daylight saving change falls in between, and then one “day” is 23 or 25 hours long and your answer comes out as 63.96. Set both dates to midnight in the same time zone and round the result, or use your language’s date library to count calendar days directly.

When you need it every day

A calculator is great for a one-off. If you keep coming back to check how many days are left until something, a countdown app does the sum for you every morning. Days Left shows the days left on your Home Screen, along with the same breakdown as the calculator above: weeks and days, hours and weekends.

9:41

For the end of the year specifically, there’s a live year progress page, and a Christmas countdown that counts weeks, weekends and sleeps.

Quick answers