Age Calculator

How this calculation works

Exact age is calculated by subtracting the birth date from the comparison date, borrowing across month and year boundaries when the day-of-month is negative.

This calculator also returns total days and hours lived — useful for milestone tracking, insurance age rules, and eligibility windows.

How this Age Calculator works — 2026 guide

Age in years isn't always enough — insurance quotes, benefit eligibility, sports leagues, and milestone planning often hinge on exact age in years, months, and days. This age calculator takes a birth date and a comparison date and computes the precise elapsed time, borrowing across month and year boundaries exactly like a calendar does (so February 29 leap-day birthdays are handled correctly). It also returns the total days and hours lived, which is surprisingly handy for "1000 days until retirement" style goals.

How to use it in 3 steps

1. Enter the birth date and (optionally) the comparison date — today is the default.
2. The calculator subtracts dates with calendar borrowing to get years, months, and days.
3. Read total days, hours, and a quick age-in-months figure for eligibility checks.

Who this is for

Parents tracking milestones, anyone applying for age-based benefits or insurance, and students solving "how many days old am I" math. Pair it with the [work day counter](/tools/work-day-counter/) for deadline math and the [project deadline calculator](/tools/project-deadline-countdown-calculator/) for date arithmetic.

Data sources & authoritative references

This calculator is built on official U.S. rules and published statistics. Key sources:

• NIST — Calendars and Timekeeping
• SSA — Age Requirements for Retirement Benefits