Leap Year & Calendar Calculator
About Leap Year Checker
The Gregorian & Astronomical Leap Year Checker determines whether any past, present, or future year is a 366-day Leap Year using Gregorian calendar rules, displaying complete divisibility proofs and adjacent leap year timelines.
How to Use Leap Year Checker
Step 1
Enter any calendar year (e.g. `2024` or `2100`).
Step 2
Click "Check Leap Year".
Step 3
Review the leap year status, total days (365 vs 366), and century rule proof.
Step 4
Click "Copy Result".
Practical Use Cases for Leap Year Checker
Software Development & Date Logic Validation
Verify leap year edge cases in billing software, date pickers, and leap day (February 29) birthday logic.
Historical Calendar & Genealogy Research
Check whether historical milestone years (e.g. 1900, 2000, 2100) contained 365 or 366 calendar days.
Input & Output Examples
Checking Year 2000 vs Year 1900
Year: 2000
Year 2000 IS a Leap Year (366 Days | Divisible by 400: Century Rule Exception Passed)
Key Features & Performance
- ✓Applies the complete 3-step Gregorian Leap Year Algorithm: Divisible by 4, except Century years unless divisible by 400.
- ✓Displays full mathematical divisibility breakdown (Year $\\bmod 4$, Year $\\bmod 100$, Year $\\bmod 400$).
- ✓Calculates Nearest Preceding Leap Year and Nearest Next Leap Year.
- ✓100% Client-Side calculation.
- ✓1-Click Copy leap year verdict.
Key Terminology & Definitions
Gregorian Century Leap Year Rule
A century year (ending in 00) is a leap year ONLY if it is evenly divisible by 400 (e.g. 2000 was a leap year; 1900 and 2100 are not).
Solar Year (Tropical Year)
The time taken by the Earth to orbit the Sun: approximately $365.2422$ days, necessitating leap days to prevent seasonal drift.