Leap Year Checker
Select a calculation mode and enter year(s) to check
How It Works
The Gregorian calendar rule: A year is a leap year if divisible by 4, except century years, which must be divisible by 400. This corrects Earth's orbit time (~365.2422 days).
Common Examples
2024: Leap year (÷4 ✓). 1900: Not leap year (÷100 but not ÷400). 2000: Leap year (÷400 ✓). 2100: Will not be leap year (÷100 but not ÷400).
Always Accessible
Works completely in your browser - no data sent to servers. Use it anytime, anywhere with full privacy protection. No year data is stored or transmitted.
How the Leap Year Checker Works
- Input Your Year: Enter a year between 1582 (Gregorian calendar adoption) and 9999. The tool validates your input for correctness.
- Select Calculation Mode: Choose between checking a single year, scanning a year range, or finding the next leap years.
- Rule Application: The tool applies the Gregorian calendar rule: (year ÷ 4 = 0) AND (year ÷ 100 ≠ 0 OR year ÷ 400 = 0).
- Exception Handling: Special handling for century years: 1700, 1800, 1900 = not leap years; 1600, 2000, 2400 = leap years.
- Result Calculation: For range checks, each year in the interval is tested individually. For next leap years, sequential years are checked until the count is met.
- Detailed Output: Results show the leap year status with a rule breakdown explaining why each test passed or failed.
Leap Year Rules & Logic
Complete Rule
IF (year % 4 == 0) AND ((year % 100 != 0) OR (year % 400 == 0)) THEN leap_year = TRUE ELSE leap_year = FALSE
Step 1: Divisible by 4
First check: year ÷ 4 must have remainder 0. This catches most leap years (e.g., 2020, 2024, 2028).
Step 2: Century Exception
If year ÷ 100 has remainder 0, it's a century year. These are NOT leap years unless they pass step 3.
Step 3: 400-Year Rule
Century years ÷ 400 must have remainder 0 to be leap years. This corrects the overcompensation from step 1.
Step-by-Step Examples
Example 1: Year 2024 (Standard Leap Year)
2. 2024 ÷ 100 = 20.24 (remainder 24) ✓ NOT a century year
3. Skip century year check
Result: LEAP YEAR ✓
Example 2: Year 1900 (Common Century Year)
2. 1900 ÷ 100 = 19 (remainder 0) ✗ Century year exception applies
3. 1900 ÷ 400 = 4.75 (remainder 300) ✗ NOT divisible by 400
Result: COMMON YEAR ✗
Example 3: Year 2000 (Century Leap Year)
2. 2000 ÷ 100 = 20 (remainder 0) ✗ Century year exception applies
3. 2000 ÷ 400 = 5 (remainder 0) ✓ Divisible by 400
Result: LEAP YEAR ✓
Practical Use Cases
Leap year checking is essential for accurate date calculations across multiple fields. Understanding and verifying leap years prevents errors in scheduling, contracts, and software systems.
Software Development & Programming
Developers must handle leap years correctly in date libraries, calendar applications, and scheduling algorithms:
- Date Validation: Ensuring February 29th is only valid in leap years
- Calendar Systems: Building accurate monthly and yearly calendar displays
- Scheduling Algorithms: Calculating future dates accurately across year boundaries
- Database Design: Storing and querying date-based information correctly
Financial & Legal Applications
Financial calculations and legal contracts often depend on precise day counts:
- Interest Calculations: Daily interest accrual over multiple years must account for 366-day leap years
- Contract Duration: Multi-year agreements with specific end dates
- Lease Agreements: Rental periods spanning leap years
- Bond Maturities: Financial instruments with exact maturity dates
Event Planning & Scheduling
Long-term planning requires accurate calendar understanding:
- Recurring Events: Annual events falling on specific dates
- Project Timelines: Multi-year projects with milestone dates
- Historical Research: Aligning historical dates with modern calendars
- Birthday Calculations: For those born on February 29th