SEOAnalytics Lab

How to Calculate the Days Between Two Dates (With Examples)

By SEOAnalytics Lab · Updated · 6 min read

How many days are left until a deadline, an exam or a trip? When is an invoice due if it must be paid in 30 days? Questions like these look easy, but months have different lengths, leap years add a day and it is easy to be off by one. A small method and a good calculator remove the guesswork.

This guide shows how to count the days between two dates by hand, how to add or subtract days and months, how to decide whether to include the end date and how leap years and weekends change the result.

What does it mean to calculate days between dates?

Calculating the days between two dates means finding how many days pass from the earlier date to the later one. The answer can also be shown in weeks, months or years, and sometimes you only want to count working days.

The tool on this page does the counting for you, and it also lets you add or subtract time from a date to find a new date.

How to calculate the days between two dates by hand

Count the days left in the first month, add the full months in between and then add the days of the last month. For example, from 1 March 2026 to 1 June 2026 is 31 + 30 + 31 = 92 days (March, April and May). From 1 June to 15 June is 14 more days, so 1 March to 15 June is 106 days, or 15 weeks and 1 day.

Another example: from 10 October 2026 to 25 December 2026 is 21 days left in October, 30 days in November and 25 days in December, which makes 76 days, or 10 weeks and 6 days.

Step-by-step: using the date calculator

  • Step 1: Choose the tool. Pick Days between two dates, or Add or subtract time.
  • Step 2: Enter your dates. Choose the dates, or press Use today to fill in the current date.
  • Step 3: Decide about the end date. Tick the option if the last day should be counted as well.
  • Step 4: For the second tool. Choose Add or Subtract and enter the years, months, weeks and days.
  • Step 5: Read the result. Copy it, or clear the form to start again.

Include the end date or not?

By default the difference between two dates does not count the last day. From 1 January to 7 January is 6 days. If you count both the first and the last day, as you might for a hotel stay or a course, the same range is 7 days.

Decide which rule you need before you start, and write it down, so that everyone who reads the number understands it the same way.

Adding and subtracting days, weeks and months

  • 30 days after 1 January 2026. 31 January 2026.
  • 90 days after 1 January 2026. 1 April 2026, a Wednesday.
  • 6 weeks before 15 June 2026. 4 May 2026.
  • An invoice due in 30 days. If the invoice is dated 15 October 2026, the due date is 14 November 2026.
  • 1 month after 31 January. 28 February in a normal year, or 29 February in a leap year, because February has no 31st.

Weeks, weekdays and weekend days

Any 14 days in a row contain 10 weekdays and 4 weekend days, so two weeks of 14 days are 10 working days. For a range that is not a whole number of weeks, the tool shows the weekdays and the weekend days separately.

Public holidays are not removed, because they differ from country to country. Subtract them yourself if your deadline is counted in working days.

How leap years change the result

A leap year has 366 days because February has 29 days. From 1 March 2026 to 1 March 2027 is 365 days, but from 1 March 2027 to 1 March 2028 is 366 days, because it includes 29 February 2028.

A year is a leap year if it can be divided by 4, except for century years, which must also be divisible by 400. So 2028 is a leap year, 2000 was one and 1900 was not.

When do you need to count days?

  • Deadlines and projects. Find how many days or working days are left until a due date.
  • Payment terms. Work out the due date of an invoice that must be paid in 30, 45 or 60 days.
  • Notice periods. Check the last day of a notice period. A 30-day notice that starts on 20 November 2026 ends on 20 December 2026.
  • Returns and warranties. See whether a 14, 30 or 90 day window is still open.
  • Travel and events. Count the days of a trip or count down to a wedding, a birthday or an anniversary.

Common date calculation mistakes

  • Treating every month as 30 days. Months have 28 to 31 days, so multiplying months by 30 gives a wrong total.
  • Forgetting leap days. A range that crosses 29 February has one extra day.
  • Counting the end date by accident. Decide first whether the last day should be included.
  • Mixing up date formats. The date 04/10/2026 means 4 October in many countries and 10 April in others, so always check the format.
  • Ignoring weekends and holidays. A deadline in working days is shorter than the same number of calendar days.

Calculate your dates now

Use our free date calculator to count the days between two dates, or to add and subtract time. Your dates stay in your browser and are never uploaded. You can also find your exact age with the Age Calculator.

Frequently asked questions

How do I calculate the number of days between two dates?

Subtract the earlier date from the later one, or count the days left in the first month, the full months in between and the days of the last month. A date calculator does it in one step.

Does the calculation include the end date?

Not by default, so 1 January to 7 January is 6 days. Tick the option to include the last day and it becomes 7.

How do I add days to a date?

Use the Add or subtract tab, pick the start date, choose Add and enter the number of days. For example, 30 days after 1 January 2026 is 31 January 2026.

Does it count weekends and holidays?

The total counts every day and also shows the weekdays and weekend days separately. Public holidays are not removed because they differ by country.

More guides