Year Calculator
Operation Type
Start Date
→
End Date
Start Date
Years to Add
Enter dates and click 'Calculate' to see the result.
How to Use the Calculator
Select Operation: Choose 'Add Years', 'Subtract Years', or 'Years Between' using the radio buttons.
Enter Dates: Click the input fields to open a date picker or type the date manually.
Calculate: Hit the 'Calculate' button to see the result instantly in the result box.
Calculation Logic
// For 'Years Between'
function getFullYears(startDate, endDate) {
let years = endDate.getYear() - startDate.getYear();
if (endDate.getMonth() < startDate.getMonth()) {
years--;
}
return years;
}
// For 'Add/Subtract'
function addYears(date, years) {
date.setFullYear(date.getFullYear() + years);
return date; // JS handles leap years!
}
Understanding Leap Year
A leap year occurs every 4 years to keep our calendar in sync with the Earth's revolutions around the Sun. This extra day is February 29th. The rules are:
A year is a leap year if it is divisible by 4.
However, if the year is divisible by 100, it is NOT a leap year...
...UNLESS it is also divisible by 400.
A Timeline of Calendars
~3100 BC
The ancient Egyptians develop a 365-day calendar, one of the first to be based on the solar year.
45 BC
Julius Caesar introduces the Julian Calendar, which includes the concept of a leap year every four years.
1582 AD
Pope Gregory XIII introduces the Gregorian Calendar, the system we use today, which refines the leap year rule for better accuracy.
Practical Applications
Age Calculation
Quickly find the precise age of a person or the age of an object.
Contract & Warranty
Determine the end date of contracts, warranties, or subscriptions.
Historical Events
Calculate the time passed since a significant historical event.
Date Formats Around the World
Region
Common Format
USA
MM/DD/YYYY
Most of Europe
DD.MM.YYYY
China / Japan
YYYY-MM-DD
International Standard
YYYY-MM-DD (ISO 8601)
Fun Facts About Years
A "galactic year" is the time it takes our Solar System to orbit the center of the Milky Way—about 230 million Earth years!
The concept of "New Year's Day" on January 1st was established by the Roman calendar. Before that, it was often celebrated in March.
Frequently Asked Questions
Why does 'Years Between' sometimes give a different result than just subtracting years? +
Our calculator determines the number of *full years* that have passed. For example, from Dec 31, 2023, to Jan 1, 2024, only one day has passed, so zero full years. The calculator accounts for the month and day for better accuracy.
How does adding a year to February 29th work? +
If you add one year to Feb 29, 2024, the result will be Feb 28, 2025. The calculator's logic correctly adjusts for the non-existent date in the target non-leap year.