Year Calculator: Easily Compute Time Spans Between Two Dates

How to use the tool

• Select a start date—for instance 20 Feb 1995 or 14 Jul 2008.
• Select an end date—for example 05 Aug 2022 or 25 Apr 2023. The end date must be later.
• Press “Calculate Years” to see two results:
  • Full years: complete anniversaries passed.
  • Exact years: fractional value that includes extra days.

Formulas used

JavaScript converts each entry to a UTC time-stamp, subtracts, and then applies:

$$\text{FullYears}=End_{Y}-Start_{Y}-\begin{cases}1,&End_{md}

$$\text{ExactYears}=rac{End_{ms}-Start_{ms}}{1000\cdot60\cdot60\cdot24}\;/\;365.25$$

Example 1

• Start Date: 20 Feb 1995
• End Date: 05 Aug 2022
• Full Years: 27 years
• Exact Years: 27.45 years (166 days ÷ 365.25)

Example 2

• Start Date: 10 Nov 2010
• End Date: 25 Apr 2023
• Full Years: 12 years
• Exact Years: 12.45 years (166 days ÷ 365.25)

Quick-Facts

• The Gregorian mean year is 365.2425 days (US Naval Observatory, 2020).
• There are 97 leap years in every 400-year cycle (ISO 8601:2019).
• JavaScript Date reliably handles years ± 100,000 (MDN Web Docs, 2023).
• Age-restricted sales in the U.S. require proof of 18 full years (US Code § 201, 2022).

FAQ

What does the Year Calculator do?

It computes the time between two calendar dates and returns both complete and fractional years, updating instantly in your browser (MDN, 2023).

How are full years different from exact years?

Full years count whole anniversaries only, while exact years divide the precise day-difference by 365.25 to include partial years (USNO, 2020).

How does the tool treat leap years?

Leap days automatically extend February when the year meets the “divisible by 4, except centuries not divisible by 400” rule (ISO 8601:2019).

What date range can I enter?

JavaScript’s Date object supports roughly ±100,000 years, far beyond typical historical or future planning needs (MDN, 2023).

Why divide by 365.25?

Using 365.25 approximates the leap-year cycle: four years average an extra day, giving “a remarkably close mean length,” according to the US Naval Observatory.

Can I convert exact years to months?

Multiply the exact years result by 12 to estimate months; for days, multiply by 365.25 (ISO 8601:2019).

How precise are the outputs?

The calculator rounds exact years to two decimals—±1 day accuracy—which suits project planning, HR records, and age verification (OECD Project Guidelines, 2021).

How do I embed this on my site?

Copy the HTML+JavaScript block into any WordPress or static page; it runs client-side, so no server configuration is needed (WordPress Dev Docs, 2023).