About the Years Between Dates Calculator
How many years has someone worked for a company? How long ago was a building built? How old is a car, a tree, a marriage or a mortgage? The years between dates calculator measures the span between two dates in years — as whole years, as decimal years, and as a full years, months and days breakdown — along with the total days and the number of leap days the range crosses.
Whole years are what people usually mean by anniversaries and length of service. Decimal years are useful for pro-rata calculations, growth rates and averages. The calculator gives both, calculated exactly from the calendar rather than by dividing days by 365.
How to Use the Years Between Dates Calculator
Enter the start date and the end date, in either order.
The result appears immediately.
How Years Are Counted
whole years: anniversaries of the start date on or before the end date
decimal years: whole years + days since the last anniversary
÷ days until the next anniversary
leap days: 29 Februaries from the start date up to the end date
a start date of 29 February has anniversaries on 28 February in common yearsStep-by-Step Example
From 1 June 2010 to 29 September 2026.
Anniversaries: 1 June 2011 … 1 June 2026 → 16 whole years
Leftover: 1 June 2026 → 29 September 2026 = 120 days
Next year: 1 June 2026 → 1 June 2027 = 365 days
Decimal: 16 + 120 ÷ 365 = 16.33 years
Breakdown: 16 years, 3 months and 28 days
Total days: 5,964
Leap days: 2012, 2016, 2020, 2024 → 4The span is 16 whole years, or about 16.33 years.
Whole Years and Anniversaries
The whole-years figure increases by one on each anniversary of the start date, just like an age. It is the figure used for wedding anniversaries, long-service awards, years of experience on a CV and statutory entitlements that depend on completed years of employment, such as redundancy pay or extra holiday in some countries. Someone who started on 1 June 2010 completes 16 years of service on 1 June 2026, not a day earlier.
Decimal Years
Decimal years are needed when a fraction of a year matters. Examples include pro-rata entitlements (holiday, bonuses or fees for part of a year), average annual growth (a value that doubled over 16.33 years grew at about 4.3 percent a year), depreciation of equipment, and scientific data where time is recorded as a continuous variable. The calculator measures the leftover days against the actual length of the following year, 365 or 366 days, and also shows the simpler days ÷ 365.25 figure; the two usually agree to two decimal places.
Leap Years and Leap Days
A leap year has 366 days, with the extra day on 29 February. The rule is: a year divisible by 4 is a leap year, except that a year divisible by 100 is not, unless it is also divisible by 400. So 2000 was a leap year but 1900 was not, and 2100 will not be. Over 400 years this gives 97 leap years and an average year of 365.2425 days, which keeps the calendar aligned with the seasons. The leap-day count shows how many extra days are included in the total.
Years of Service
Employers often need years of service for notice periods, pension schemes, service awards and redundancy calculations. Enter the start date and either today's date or the leaving date. Check whether your rules count completed years (the whole-years figure) or part years (the decimal figure), and whether a period of leave or a break in service should be excluded. For a leaving date that falls a few days short of an anniversary, the whole-years figure will be one lower — a detail that can affect entitlements.
Dates Before and After Anniversaries
Because whole years only change on the anniversary, two dates a day apart can give different results. From 1 June 2010, the span to 31 May 2026 is 15 whole years, but the span to 1 June 2026 is 16. The decimal figure changes smoothly instead, from 15.997 to 16.000, which is why it is preferred for calculations where a sudden jump would be unfair.
Historical Dates
The calculator uses the Gregorian calendar for every date, extended backwards. That is fine for modern dates, but countries adopted the Gregorian calendar at different times — Catholic countries in 1582, Britain and its colonies in 1752, Russia in 1918 — and dates recorded before the switch in a given country were in the older Julian calendar, which by the 18th century ran 11 days behind. For spans involving such historical dates, convert them to the Gregorian calendar first, or expect a difference of up to about two weeks. For anything in the last hundred years or so, no adjustment is needed.
Understanding Your Result
The headline gives the whole years.
The decimal years line gives the exact fractional span.
The years, months, days line gives the full breakdown.
The days line gives the total days and the 365.25-day equivalent.
The leap days line counts the 29 Februaries crossed.
When Should You Use This Calculator?
Use it to calculate years of service or experience.
Use it to find the age of a building, vehicle or investment.
Use it for anniversaries and milestones.
Use it for pro-rata and growth-rate calculations that need decimal years.
Common Mistakes
Dividing days by 365. Leap days make this slightly high over long spans.
Rounding up a year that is not complete. Completed years change only on the anniversary.
Forgetting century leap-year rules. 1900 and 2100 are not leap years.
Mixing up the date format. Enter dates as year-month-day.
Ignoring the leaving date. Service ending a day before an anniversary counts one fewer whole year.