This guide covers How to Calculate Days Between Two Dates | TimeFlow — what it means, how it works, and how to use it. The explanations below are followed by worked examples with real dates and real times, a set of frequently asked questions, and links to the tools that do the calculation for you: the time zone converter, the world clock, and the UTC converter. Where a number is given — an offset, a date, a count — it is computed from the IANA Time Zone Database for the date stated, not copied from a table that may be out of date.

Try the tool: Time Zone Converter — convert any time between any two cities, with the daylight saving rules for the date you choose.

Counting the days between two dates is a subtraction, but the calendar makes it fiddly: months have different lengths, February changes with leap years, and you have to decide whether to count the start date, the end date, or both.

The standard convention — the one used by the days-between calculator on this site — is to count the number of days you have to add to the start date to reach the end date. From 1 January to 2 January is 1 day. From 1 January to 1 February is 31 days. From 1 January 2026 to 1 January 2027 is 365 days, because 2026 is not a leap year.

The method by hand is to count the remaining days in the start month, add the full months in between, and add the days in the end month. From 15 March to 20 June: 16 days left in March (31 − 15), plus 30 in April, plus 31 in May, plus 20 in June — 97 days. The calculator does the same thing, including leap years, and it also gives the answer in weeks and months.

The common mistakes are forgetting leap years (February 2028 has 29 days, not 28), counting both endpoints (which adds one day), and forgetting that the answer depends on the year. The days-between pages on this site give the exact count for specific months and date ranges, with a day-by-day calendar so you can check the result.

In practice

The method is to count the days you add to the start date to reach the end date. From 1 January to 11 January is 10 days — you add 10 days to the 1st to reach the 11th. The start day itself is not counted, and that is the convention every calculator uses. If you want the inclusive count — counting both the first and the last day — add one.

The fiddly part is the months. January has 31 days, February has 28 or 29, and the rest alternate — and the only way to be sure is to count month by month, or to let a calculator do it. The days between dates calculator counts the days, weeks and months between any two dates, and the date calculator works out what date it is a number of days from now.

The commonest use is the simplest: how long until something. A holiday, a deadline, a birthday, a visa expiry — all of them are a date difference, and all of them are easier with a calculator than with a calendar. The holiday countdowns show the countdown to every major holiday live, and the countdown timer counts down to any date you choose.

The numbers: the year 2026

2026 is not a leap year: it has 365 days, 52 full weeks and one extra day, and 53 ISO weeks (because it starts on a Thursday). There are 261 weekdays in the year and 104 weekend days. The next leap year is 2028, and the one after that is 2032; the century year 2100 will not be a leap year, because it is divisible by 100 but not by 400. 1 January 2026 was a Thursday, and 31 December 2026 will be a Thursday.

The extra day is the reason the calendar shifts: because 365 days is 52 weeks and one day, every date falls one weekday later the following year — two days later after a leap year. That is why your birthday is on a different weekday almost every year, and why the calendar repeats every 28 years in most cases. The week number finder gives the ISO week for any date, the date calculator works out what date it is a number of days from now, and the days between dates calculator counts the days between any two dates.

2027 is also not a leap year: it has 365 days, 52 ISO weeks, and 261 weekdays. It starts on a Friday and ends on a Friday. The next leap year after 2026 is 2028, which will have 366 days and 262 weekdays. The business days calculator counts the business days in any year, with the public holidays subtracted.

Key facts

  • A normal year has 365 days and a leap year has 366, with the extra day on 29 February.
  • A year has 52 full weeks and one extra day — or two in a leap year.
  • The Gregorian leap year rule: divisible by 4, except centuries, except centuries divisible by 400.
  • A business day is a weekday that is not a public holiday — and the holidays depend on the country.
  • In the ISO week system, the week starts on Monday and the first week is the one containing the first Thursday.

Frequently asked questions

How do I calculate days between two dates?

Count the days you add to the start date to reach the end date. From 1 January to 11 January is 10 days. The days between dates calculator does it for any two dates.

Is the start day counted?

No, by the standard convention. If you want the inclusive count — counting both the first and the last day — add one to the result.

How do I count months between two dates?

Count the full months, then the remaining days. Months have different lengths, so the only reliable way is to count month by month, or to use a calculator.

How many days are between 1 January and 1 December 2026?

334 days. 2026 is not a leap year, so the year has 365 days, and 1 December is the 335th day.

What is the difference between calendar days and business days?

Calendar days count every day; business days count only weekdays that are not public holidays. Ten business days from a Monday is a fortnight later; ten calendar days is ten days later.

How many weekdays are there in 2026?

261 weekdays and 104 weekend days, out of 365 days in total. 2026 is not a leap year. The business days calculator counts the business days, with the public holidays subtracted.

What is the time difference between London and Tokyo?

Nine hours in January 2026: London is UTC+00:00 and Tokyo is UTC+09:00. In July it is eight hours, because London moves to UTC+01:00 while Tokyo stays on UTC+09:00. The time zone converter gives the difference for any two cities and any date.

Related pages

Sources

  • IANA Time Zone Database, via Node.js Intl (Intl.DateTimeFormat with timeZone) — offsets, daylight saving dates and local times in this article were worked out from the IANA database, not typed from memory.
  • TimeFlow's own time-zone data (data/cities.ts, data/dst.ts), computed from the IANA database.
  • Time zone rules and offsets: the IANA Time Zone Database, as applied by this site's tools. Offsets and daylight saving dates on this page are computed from the database for the dates stated.
  • TimeFlow's time zone converter, world clock and UTC converter — the live tools behind the numbers on this page.
  • Time-zone and daylight saving rules are set by governments and can change. For flights, deadlines and meetings that cannot move, confirm the time with an official source.