This guide covers Why Do We Have Leap Years? | 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a count — it is computed from the IANA Time Zone Database for the date stated, not copied from a table that may be out of date.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.

We have leap years because the Earth's orbit does not divide neatly into days. A year — one orbit of the Sun — takes about 365.2422 days. A calendar year has to be a whole number of days, so the Gregorian calendar uses 365 days and adds an extra day every four years to catch up the missing quarter-days.

Without the correction, the calendar would drift. After one year the calendar would be a quarter of a day behind the seasons; after 100 years it would be 24 days behind; after 700 years the seasons would be reversed — Christmas would fall in summer in the Northern Hemisphere. This actually happened under the old Julian calendar, which added a leap day every four years without exception: by 1582 the calendar had drifted 10 days, and Pope Gregory XIII had to delete 10 days from October to fix it.

The Gregorian rule — leap years every four years, except century years unless divisible by 400 — is a refinement. It removes three leap days every 400 years, which brings the average year to 365.2425 days, very close to the true 365.2422. The remaining error is about one day in 3,300 years, which is good enough that no one alive needs to worry about it.

The extra day is 29 February, and it is the reason that dates like 29 February 2000 exist but 29 February 1900 and 2100 do not. Anyone doing date arithmetic — age calculators, countdowns, contract dates — has to get this rule right, because the century exceptions are the ones people forget.

In practice

Without leap years, the calendar would drift away from the seasons, and the drift would be fast. The Earth's orbit takes 365.2422 days, so a 365-day calendar loses almost six hours a year. After four years the calendar is a day behind; after a century it is 24 days behind; after 400 years it is three months behind. Christmas would fall in autumn, and the summer solstice would fall in spring. Leap years are the fix.

The fix is not perfect, and that is why the century rule exists. Adding a day every four years overcorrects by about 11 minutes a year — the real year is slightly less than 365.25 days — so the Gregorian rule skips the leap day in century years, except those divisible by 400. The result is a calendar that gains only one day every 3,300 years, which is accurate enough for any practical purpose.

The seasons are the reason it matters. The calendar is tied to the Earth's orbit, and the orbit is tied to the seasons: the solstices and equinoxes fall on nearly the same dates every year because of the leap year rule. Farmers, astronomers and anyone who plans around the seasons all depend on it. The leap year is not a quirk; it is the mechanism that keeps the calendar honest.

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

Why do we have leap years?

Because the Earth's orbit takes 365.2422 days, not 365. A 365-day calendar loses almost six hours a year, so we add a day every four years to catch up.

What happens without leap years?

The calendar drifts away from the seasons: after four years it is a day behind, after a century it is 24 days behind, and after 400 years it is three months behind. Christmas would fall in autumn.

Why is there a century rule?

Adding a day every four years overcorrects by about 11 minutes a year, so the Gregorian rule skips the leap day in century years — except those divisible by 400. The result gains only one day every 3,300 years.

How long is a year, exactly?

365 days, 5 hours, 48 minutes and 45 seconds — 365.2422 days. That is the tropical year, measured from one spring equinox to the next.

Do all calendars have leap years?

No. The Islamic calendar is lunar — twelve moons, about 354 days — and has no leap years, which is why Ramadan falls about 11 days earlier each year.

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.