Check If Any Year Is a Leap Year Check if any year is a leap year and see the mathematical rules explained.
Leap Year Checker
Check if any year is a leap year and see the mathematical rules explained.
Enter a Year
Type any year into the input field.
View the leap year result and rule breakdown
Instantly see whether it's a leap year with the rules explained.
Explore Range
Find all leap years within any custom year range.
What Is Leap Year Checker?
The Leap Year Checker instantly tells you whether any given year is a leap year, along with a detailed explanation of which rules it passes or fails. It shows the number of days in the year (365 or 366), the number of days in February (28 or 29), and the previous and next leap years. A step-by-step breakdown shows the three leap year rules: divisible by 4, not divisible by 100, or divisible by 400. A range finder lets you discover all leap years within any custom range, displaying them as clickable buttons. This is useful for calendar planning, educational purposes, date validation, and understanding the Gregorian calendar system.
Why Use Leap Year Checker?
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Instant leap year verification for any year
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Step-by-step rule explanation with pass/fail indicators
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Previous and next leap year lookup
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Custom range finder to list all leap years in a period
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Educational display of the three leap year rules
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Handles the 100/400 exception correctly
Common Use Cases
Calendar Development
Validate date calculations in software that handles leap years.
Education
Teach students the leap year rules with visual step-by-step breakdown.
Historical Research
Determine if historical dates fell in leap years for accurate calendaring.
Birthday Planning
Check if someone born on February 29 has a "real" birthday in a given year.
Data Validation
Verify February 29 dates in datasets are valid by checking the leap year status.
Technical Guide
The leap year check implements the Gregorian calendar rule: a year is a leap year if it is divisible by 4 AND (not divisible by 100 OR divisible by 400). In JavaScript: (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0. The previous/next leap year finders use simple while loops that increment/decrement from the current year until they find a year passing the test. The range finder iterates through the specified range and collects all leap years into an array. The explanation string is dynamically generated based on which divisibility conditions the year meets, providing specific reasoning like "2000 is divisible by 400" or "1900 is divisible by 100 but not by 400".
Tips & Best Practices
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1Century years like 1900 are NOT leap years, but years divisible by 400 (like 2000) ARE
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2Use the range finder to quickly list all leap years in a decade or century
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3Click any leap year in the range results to check its details
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4The next leap year is useful for February 29 birthday planning
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5Remember: leap years add February 29, making the year 366 days long
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📅 Date & TimeFrequently Asked Questions
Q What are the leap year rules?
Q Why do we have leap years?
Q How often do leap years occur?
Q Is year 0 a leap year?
Q What happens to people born on February 29?
About This Tool
Leap Year Checker is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.