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When Is a Leap Year? Calculator

The /4, /100, /400 rule stated in three plain lines, the date of the next 29 February with a live countdown, and the number of days February has for each of the next ten years.

Related tools

All Dates & time tools →
Leap Year CalculatorCheck whether any year is a leap year with the /4, /100, /400 rule shown step by step, plus the previous and next leap years, the days left until 29 February and the Julian-calendar caveat before 1582.Next Leap Year CalculatorThe next leap year after any year you enter, the twelve that follow, and the gap between each one — including the eight-year jump from 2096 to 2104 that most people never notice.Leap Years List CalculatorList every leap year in the range you choose, with the count, the century exceptions highlighted (1700, 1800 and 1900 skipped; 1600 and 2000 kept) and a one-click copy of the whole list.Day of the Year CalculatorThe ordinal day number of any date — the ISO 8601 ordinal format — with the days remaining, the ISO week, the quarter, the weekday, the percentage of the year elapsed, and the month-by-month addition shown in full.Day of Year CalendarA full year on one page: twelve month blocks where every cell carries its day-of-year number from 1 to 365 or 366, today highlighted, and each date's ISO week, quarter and days remaining one click away.Longest Day of the Year CalculatorHow long the longest day actually lasts at your latitude, how many minutes more daylight that is than at the equinox, the ten longest days of the year and the month-by-month curve — June solstice in the north, December in the south.Shortest Day of the Year CalculatorHow little daylight the shortest day leaves at your latitude, how many minutes less that is than at the equinox, polar night counted day by day, and the ten shortest days of the year — December solstice in the north, June in the south.Anniversary CalculatorHow long has it been, exactly? Years, months and days elapsed since a wedding, a first date, a friendship or a first day at work, the total in days, weeks and hours, the countdown to the next anniversary, the milestones coming up (10 000 days, silver, gold) and — for weddings — the traditional and modern gift for that year, in both the British and the American lists.

When Is a Leap Year? Calculator works straight from this page — free, instant, nothing to install. It sits under Dates & time in our catalogue, alongside Leap Year Calculator and Next Leap Year Calculator.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What does When Is a Leap Year? Calculator do?

The /4, /100, /400 rule stated in three plain lines, the date of the next 29 February with a live countdown, and the number of days February has for each of the next ten years.

When would I actually use this?

Answering a scheduling question exactly: how many working days until a deadline, what date falls sixty days out, and what time that is for a colleague elsewhere.

What is the most common mistake?

Counting days by subtracting dates and forgetting whether the endpoints are included. Inclusive and exclusive counts differ by one, which is the difference between meeting a deadline and missing it.

How is When Is a Leap Year? Calculator different from Leap Year Calculator?

They sit next to each other but answer different questions: Leap Year Calculator is the one to open when you need it to check whether any year is a leap year with the /4, /100, /400 rule shown step by step, plus the previous and next leap years, the days left until 29 February and the Julian-calendar caveat before 1582. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Next Leap Year Calculator is the closest one after this: The next leap year after any year you enter, the twelve that follow, and the gap between each one — including the eight-year jump from 2096 to 2104 that most people never notice.

What else is worth having open alongside it?

Leap Years List Calculator and Day of the Year Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

Calendar arithmetic follows the proleptic Gregorian calendar and the IANA time-zone database, so daylight-saving transitions and leap years are handled. Public holidays vary by country and region and are not assumed.

Further reading

All guides →
ExplainerLeap Years: The Rule, the Exception, and the Exception to the ExceptionDivisible by four, except centuries, except centuries divisible by four hundred. The three-line rule exists because the tropical year is not 365.25 days, and the arithmetic behind it explains ten deleted days in 1582 and a calendar that repeats exactly every 400 years.ExplainerWorking Out an AnniversaryCounting back and counting forward are two different sums, and they disagree by a year on the day itself. What this calculator does with 29 February, what other date libraries do, and where the traditional and modern gift lists actually come from.ExplainerDate Arithmetic Is Harder Than It Looks"One month later" has no single correct answer, and every date library has had to pick one. Month addition is neither associative nor invertible, a day is not always 24 hours, and age is not days divided by 365.25.ExplainerWhat Is a Leap Year? The /4, /100, /400 Rule ExplainedWhy some years have a February 29, how the divisible-by-4, -100 and -400 rules combine, and how to check any year quickly.How-toCountdown to New Year: How to Count the Days and Weeks LeftBuilding a countdown to a target date is just counting whole days from today to the target, then splitting that total into weeks. Learn the method with a worked example.ExplainerWhat Generation Am I? Birth-Year Cutoffs ExplainedBoomer, Gen X, Millennial, Gen Z or Alpha? Learn the commonly used birth-year ranges, why the boundaries are fuzzy, and how to place yourself if you were born near a cutoff.
When Is a Leap Year? Calculator — OneKitly