Age Calculator: Years, Months & Days

Reading your age results

Enter date of birth and an as-of date. The dark results panel shows chronological age in years, months, and days, chip totals from months through seconds, and a next-birthday countdown when the as-of date is today or earlier.

Example: Jan 1, 1990 birth, as-of today

The form defaults to January 1, 1990 with Age as of set to today, so the headline updates daily (for example, about 36 years, 5 months in mid-2026). For a fixed deadline such as a benefits form, set Age as of to that date instead of today.

Example: same birth, Dec 1, 2026 deadline

January 1, 1990 with Age as of December 1, 2026 reads 36 years, 11 months. Use that pattern when a form names a cutoff date rather than "today."

Month lengths and borrowing

Months have 28 to 31 days. When the as-of day is before your birth day, the calculator borrows one month and adds the prior month's length so years, months, and days stay calendar-accurate.

Two people? Use Age Difference

This tool measures one birth date against one as-of date. To compare two birth dates side by side, use the Age Difference Calculator.

Age Calculator: Years, Months, Days & Full Time Breakdown

This reference explains chronological age from birth through any as-of date, with calendar-accurate month lengths, leap years, and Western-age limits.

What This Age Calculator Does

Enter a birth date and an as-of date. You get chronological age in years, months, and days, expanded totals from months through seconds, and a next-birthday countdown. Set a fixed benefits or visa deadline in Age as of instead of today when a form names a cutoff date. Western rules only.

What it does not do:

No Korean age, lunar-calendar age, or insurance "age nearest birthday" rounding.

How to Calculate Age from Date of Birth

The age formula

Count complete years since birth (has the birthday passed in the as-of year?), then remaining months, then days. Real month lengths and leap years apply throughout. When the as-of day-of-month is before your birth day-of-month, borrow one month and add the prior month's length to the day count.

Leap year rule:

Divisible by 4, except century years unless divisible by 400, so 2000 was a leap year and 1900 was not. Each Feb 29 in your span counts in total days. Leap-day births use Feb 28 in non-leap years for age and next-birthday timing.

Worked example

Birth date: March 15, 1990. As-of date: January 10, 2026.

Complete years: March 15, 1990 → March 15, 2025 = 35 years (birthday has not yet occurred in 2026).
Remaining months: March 15, 2025 → January 10, 2026 = 9 months and 26 days.
Result: 35 years, 9 months, 26 days.
Total days: approximately 13,050 (the calculator counts every day including leap days).

Time units:

Both dates anchor at local midnight (00:00:00). Total days sit between those midnights; weeks, hours, minutes, and seconds are derived from that day count only (÷ 7, then × 24, × 60, × 60), not a time-of-day on either date.
Edge case, same-day birth:

If the as-of date equals the birth date, age is exactly 0 years, 0 months, 0 days.

Age Milestones and Legal Ages by Country

Medicare in the US starts at 65; a learner permit can open at 16 in some states. Set the as-of date to the program's cutoff to see if you've passed the birthday, not just whether the calendar year looks right.

United States:

Driving permit: 15–16 (varies by state). Voting and military service: 18. Alcohol purchase: 21. Full Social Security retirement: 66–67 (birth-year dependent). Medicare eligibility: 65.
United Kingdom:

Driving (car): 17. Voting: 18. Alcohol purchase: 18. State pension: 66 (rising to 67 by 2028).
Canada:

Driving: 16 (varies by province). Voting: 18. Alcohol: 18 or 19 depending on province. Canada Pension Plan: early at 60, standard at 65.
European Union (general):

Driving (car): 17–18. Voting: 18 (16 in Austria and Malta). Alcohol: 16–18 depending on country and drink type. Retirement: 62–67 depending on country.
Japan:

Age of majority was lowered from 20 to 18 in 2022. Drinking and smoking remain 20. Driving: 18. National pension: 65.
Australia:

Driving (learner permit): 16. Voting: 18 (compulsory). Alcohol: 18. Age Pension: 67.

Age Calculator FAQ

How do I calculate my age from my date of birth?

Chronological age is years, months, and days from birth date through your as-of date. If the as-of day-of-month is earlier than your birth day-of-month, the calculator borrows one month and adds the prior month's length to the day count. Feb 29 birthdays use Feb 28 in non-leap years for both age and the next-birthday countdown. The results panel also shows totals in weeks through seconds.

Why does the second date default to today?

Age as of defaults to today so age is measured through the current calendar day without picking a second date. Enter your own date of birth in the first field; the sample January 1, 1990 birth date is only a placeholder until you change it.

How do leap years affect my age in days?

Leap years add Feb 29 every four years (except most century years). Each Feb 29 in your span is counted. Example: born Feb 28, measured Mar 1 in a leap year = 2 days; in a non‑leap year = 1 day.

I was born on February 29. How is my age calculated?

Standard legal practice: leap-day birthdays count as Feb 28 in non-leap years. In 2025 (non-leap), your birthday is Feb 28 for age purposes. The Next Birthday countdown uses the same rule.

What is Western age vs Korean age?

Western chronological age counts from birth: 0 on your birth day, 1 on your first birthday. Korean age (and some East Asian systems) often counts from conception or bumps everyone on Lunar New Year, so a baby can be "1" at birth. This calculator uses the Western standard.

Can I find my age at a future or past date?

Yes. Set "Age as of" to any date. Common checks: "Will I be 59 on our plan year start?" or "How old was I on election day in 2020?"

Time & Date Reference Note

Informational Use: These tools use standard date/time algorithms and your browser’s timezone data (IANA). Results are intended for general reference and planning only.

Verification Recommended: Time zone rules and daylight saving changes vary by region and year. For critical scheduling, payroll, or legal deadlines, confirm results with official sources.

Local Verification: Always confirm times, dates, and business-day counts with official sources or qualified professionals when stakes are high.

Age Calculator: How Old Am I?

Dates

Totals