Age Calculator

How age is calculated (and why it never rounds up)

Age is the number of complete years that have passed since your date of birth. The calculator also breaks it into whole months and days, walking the calendar rather than dividing by 365. Because it counts only complete years, it never rounds up: you are not a year older until the actual birthday arrives.

Worked example: someone born on March 10, 1990 is, on October 16, 2025, exactly 35 years, 7 months and 6 days old. The math is straightforward, 2025 − 1990 = 35 years, October − March = 7 months, and 16 − 10 = 6 days. When the day subtraction would go negative, the calculator borrows a month and adds the number of days in the previous month, exactly the way you would do it on paper.

The age also shows up as totals: the same person has lived 13,004 days, or about 1,857 weeks, or roughly 312,096 hours. Those totals are useful when the calendar breakdown is not the number you need.

Years, months and days vs total days, why they differ

The years/months/days figure and the total-days figure measure two different things, and it is normal for them not to look related at a glance.

The calendar breakdown accounts for that months have different lengths and that leap years add a day. "35 years, 7 months, 6 days" is how a person would say your age. The total days figure is a straight count of days lived with no calendar structure at all, 13,004 days for the example above. Divide 13,004 by 365.25 and you get about 35.6 years, which is why the two numbers seem to disagree.

Use the calendar breakdown for anything legal, medical or official, where "age" means complete years. Use the total-days figure for milestones, "I am 10,000 days old today", and for computing an age difference between two people.

Leap-day birthdays: born on February 29

If you were born on February 29, your birthday only exists on the calendar once every four years. The convention most legal systems use, and the one this calculator follows, is to treat February 29 as falling on March 1 in common years. So someone born February 29, 2000 turns 25 on February 29, 2025 (a leap year), and their birthday is treated as March 1 in 2026 and 2027.

In practice this rarely matters for age, because the calculator counts complete years regardless of the exact birthday date, you are 26 from the moment the birthday-equivalent date passes. It matters for things like school cutoffs, driver's licence renewals and benefit eligibility, where the exact date of a birthday can shift an effective date by a day. When in doubt, check the specific rule for the jurisdiction you are dealing with. The Gregorian leap-year rule is explained in detail by the US Naval Observatory.

Two worked examples: age on a date, and a school cutoff

Example A, age on a specific date. Born March 10, 1990, as of October 16, 2025: the result is 35 years, 7 months, 6 days, which is 13,004 total days. Set the "as of" date to a past or future date to see how old you were or will be at that moment.

Example B, a kindergarten cutoff. A child is born on September 5, 2019, and the district requires children to turn 5 on or before September 1. On September 1, 2024 the child is 4 years, 11 months and 27 days old, four days short of 5. Because they have not reached the cutoff age, they start kindergarten the following year. Shifting the birth date four days earlier to September 1 would flip the answer entirely, which is exactly why the exact day matters at a cutoff.

Milestones: total days, weeks and hours alive

Some people like to track round-number milestones, the day you hit 10,000 days alive, or 20,000. Here is roughly where those land.

These assume 365.25 days a year, so they are averages. A 30-year-old has lived about 10,958 days, and a 1-year-old about 52 weeks. Enter your exact birth date above to get your precise number rather than the rounded average.

Age in the real world: retirement age and life expectancy

Age numbers matter most when they unlock something. Two of the biggest in the US are Social Security and life expectancy.

For Social Security, your full retirement age depends on your birth year: it is 67 for anyone born in 1960 or later. You can claim as early as 62, but your benefit is permanently reduced, about 30% lower at 62 than at full retirement age. Delay past your full retirement age and the benefit grows, reaching roughly 124% if you wait until 70. The rules are laid out on the SSA's retirement age page. Use the "as of" date here to see exactly how old you will be on a target retirement date.

For the bigger picture, US life expectancy at birth was 79.0 years in 2024 (76.5 for males, 81.4 for females, per the CDC), so a 30-year-old has, on average, roughly half a century ahead. Treat those as population averages, not a personal forecast, but they are the numbers behind most retirement and insurance planning.

Age on forms, IDs and eligibility rules

Different rules want your age expressed differently, and using the wrong form causes avoidable rejections.

• Government forms and applications want complete years as of the date you sign, use the whole-years figure from the top line.
• Medical and paediatric contexts often want months for young children: a 14-month-old, not "1 year." The total-months figure is the one to report.
• Benefits and cutoffs such as school entry, driver's permits or Medicare turn on a specific birthday date, so the exact day matters, not just the year.

A quick example: Medicare eligibility generally begins on the first day of the month you turn 65. Someone born August 20, 1961 turns 65 on August 20, 2026, so coverage starts August 1, 2026; someone born on the first of the month can start a month earlier. Set the as-of date above to any target date, a retirement date, a school cutoff, an enrolment deadline, to see exactly how old you will be on that day, and always confirm the specific rule with the agency, because the conventions differ between programs.