Leap Year Calculator
Leap Year Calculator
Enter any year from 1 to 9999
Enter a Year to Check
Select a mode above, then enter a year or range to instantly see if it is a leap year — with a step-by-step formula breakdown, February calendar, and more.
Check any year, explore ranges, and discover the next leap day
A leap year occurs every four years — or does it? The reality is slightly more complex, and getting it wrong can cause real calendar confusion. Our Leap Year Calculator takes the guesswork out entirely: enter any year between 1 and 9999, and you'll instantly know whether it is a leap year, how many days it has, when the next and previous leap years occur, what day of the week February 29 falls on, and a step-by-step breakdown of each divisibility rule the Gregorian calendar uses. Why does any of this matter? The Earth does not complete one trip around the Sun in exactly 365 days. The actual orbital period is approximately 365.2422 days. If we only counted 365 days every year, our calendar would drift about 24 days out of sync with the seasons every century. Leap years exist to correct that drift. By adding an extra day (February 29) roughly every four years, the Gregorian calendar stays aligned with Earth's orbit to within about 26 seconds per year — a drift of only one full day every 3,236 years. The three-rule algorithm behind leap years is elegant: a year divisible by 400 is always a leap year; a year divisible by 100 but not 400 is not a leap year; a year divisible by 4 but not 100 is a leap year; all other years are not leap years. This means the infamous year 1900 was NOT a leap year (divisible by 100 but not 400), while the year 2000 WAS a leap year (divisible by 400). The next century year that will be a leap year is 2400. Our calculator offers three powerful modes. Single Year mode gives you a complete analysis of one year — the leap status, days in February, next and previous leap years, the day of the week for Feb 29, a countdown to the next leap day from today, a visual February calendar highlighting the 29th, and a transparent step-by-step arithmetic walkthrough. Year Range mode finds every leap year between any two years you choose, shows a proportional timeline visualization, displays leap-year frequency as a donut chart, and lets you export the full list to CSV. Upcoming Leap Years mode lists the next N leap years from today — perfect for long-range planning. Whether you are a developer verifying date-handling logic, a teacher explaining calendar systems, a person born on February 29 (a 'leapling') planning milestone birthdays, or simply someone who just heard that 2100 won't be a leap year and wants to verify, this tool gives you everything you need in one place.
Understanding Leap Years
What Is a Leap Year?
A leap year is a calendar year containing one extra day — February 29 — making it 366 days long instead of the usual 365. This extra day is called a leap day. The Gregorian calendar, used by most of the world, determines leap years using three rules applied in priority order: if a year is divisible by 400, it is a leap year; if it is divisible by 100 but not 400, it is not; if it is divisible by 4 but not 100, it is a leap year; otherwise it is not. This gives us approximately 97 leap years in every 400-year cycle, keeping the calendar synchronized with Earth's solar orbit.
How Is It Calculated?
The leap year algorithm in code is: (year % 4 === 0 AND year % 100 !== 0) OR (year % 400 === 0). In plain language: start by checking if the year divides evenly by 400 — if yes, it is a leap year. If not, check if it divides by 100 — if yes, it is not a leap year (century exception). Finally, check if it divides by 4 — if yes, it is a leap year; otherwise no. This three-step check eliminates the overcorrection that a simple 'every 4 years' rule would introduce. Julius Caesar introduced the every-4-years rule in 46 BC; Pope Gregory XIII refined it in 1582 with the century exceptions we still use today.
Why Does It Matter?
Leap years affect software, finance, legal documents, and everyday life. Software bugs related to incorrect leap year handling have caused real-world failures — a notable example is the Y2K-adjacent problem where some systems assumed 1900 was a leap year when it was not. Financially, some annual interest calculations differ by one day in leap years, and salaried workers on daily-rate contracts effectively work one extra day for free. Lease and bond contracts often specify whether they use a 365-day or 366-day year. For 'leaplings' — people born on February 29 — their legal birthday in non-leap years varies by jurisdiction (some use Feb 28, others March 1).
Limitations and Notes
This calculator uses the proleptic Gregorian calendar, applying modern leap year rules to all years including those before 1582 (when the Gregorian calendar was actually adopted). Historical dates before October 1582 are typically governed by the Julian calendar, which used only the divisible-by-4 rule with no century exception — making 1500 and 1300 leap years under Julian rules but not Gregorian ones. Other calendar systems (Hebrew, Islamic, Chinese, Persian) have entirely different leap year concepts and cycles. This tool only covers the Gregorian (Western) calendar rules.
How to Use the Leap Year Calculator
Choose a Mode
Select one of three modes at the top: Single Year to check one specific year, Year Range to find all leap years between two years, or Upcoming Leap Years to list the next N leap years from today.
Enter Your Year or Range
For Single Year mode, type any year from 1 to 9999 — or click 'Current Year' to auto-fill the current year, or 'Random Year' for a surprise. For Year Range, enter start and end years or click a preset button (e.g., 2000–2100).
Read the Results
Single Year results include: leap status, days in year, days in February, next and previous leap years, day of the week for Feb 29, countdown to the next leap day, and a step-by-step arithmetic walkthrough of all three Gregorian rules.
Export or Share
Click 'Copy' to copy the summary to clipboard, 'Share' to share via the Web Share API or clipboard, 'Export CSV' to download a spreadsheet of all leap years in a range, or 'Print' to get a print-friendly version of the results.
Frequently Asked Questions
Is 2024 a leap year?
Yes, 2024 is a leap year. It is divisible by 4 (2024 ÷ 4 = 506 exactly) and not divisible by 100, so it satisfies the standard leap year rule. February 2024 had 29 days. The next leap year after 2024 is 2028, and the one after that is 2032.
Was 1900 a leap year?
No, 1900 was not a leap year — and this is one of the most common misconceptions. Although 1900 is divisible by 4, it is also divisible by 100. Under Gregorian calendar rules, century years (divisible by 100) are only leap years if they are also divisible by 400. Since 1900 ÷ 400 = 4.75 (not a whole number), 1900 was not a leap year. By contrast, the year 2000 WAS a leap year because 2000 ÷ 400 = 5 exactly.
When is the next leap year?
The next leap year after 2024 is 2028. After that, the pattern continues with 2032, 2036, 2040, 2044, 2048, and so on — every four years — until 2096. Then 2100 will NOT be a leap year (divisible by 100 but not 400), and the next leap year after 2096 will be 2104. Our Upcoming Leap Years mode lists the next N leap years automatically from today's date.
What is a leapling?
A leapling (also called a leaper) is a person born on February 29. Because this date only appears on the calendar every four years, leaplings cannot celebrate their exact birthday most years. In practice, they choose either February 28 or March 1 for non-leap-year celebrations. Some jurisdictions legally recognize March 1 as their official birthday for documents like driver's licenses. There are approximately 5 million leaplings worldwide — about 1 in every 1,461 people.
Why does the Gregorian calendar have a century exception?
Adding one extra day every 4 years slightly overcorrects. Earth's orbital year is ~365.2422 days, so a simple every-4-years rule would add too much by about 0.0078 days per year. Over 100 years, that overcorrection adds up to nearly a day. The century exception (skipping a leap year every 100 years) compensates for this. But skipping every century year would undercorrect slightly, so the 400-year exception (2000, 2400) adds back one day every 400 years. The result: a calendar that is accurate to within about 26 seconds per year.
What happens to leap year birthdays in legal and financial contexts?
Legal and financial systems handle leap day birthdays differently depending on jurisdiction. For age calculations (reaching voting age, retirement age, etc.), most legal systems treat February 28 or March 1 of a non-leap year as the equivalent of February 29. Financially, some bond and loan contracts specify either a 365-day year convention or an 'actual/actual' convention that accounts for the real number of days. Software developers must explicitly handle February 29 in date arithmetic to avoid errors — a common source of bugs in calendar and scheduling applications.