How are leap years handled?

The Gregorian calendar’s leap-year rules are applied, so 29 February and differing month lengths are counted correctly.

Age Calculator

Calculate calendar age and total elapsed days as of a chosen date.

01 / INPUTS

Date of birthAs-of date

02 / RESULT

Calendar age: 26 years, 7 months, 8 days
Total days: 9717 days

Calculation trace

2000-01-15 to 2026-08-23 = 26 years, 7 months, 8 days
26y 7m 8d
Calendar age
UTC date difference = 9,717 days
9717 days
Total days

How it works

The tool parses both dates as ISO 8601 calendar dates and computes the difference in whole years, months and days on the proleptic Gregorian calendar, plus the total number of days elapsed.

Assumptions & limits

Uses civil calendar dates (no time zones or times of day).
Months and years vary in length, so “months” reflects calendar months, not fixed 30-day periods.

FAQ

How are leap years handled?: The Gregorian calendar’s leap-year rules are applied, so 29 February and differing month lengths are counted correctly.

Related calculators

SOURCES

International Organization for Standardization (ISO)
ISO 8601 — Date and time format ↗
Calendar date representation used to parse dates and compute civil year/month/day and total-day differences on the proleptic Gregorian calendar
Accessed 2026-08-19