How is age calculated?
Exact age is computed by counting whole years from your date of birth to the target date, then whole months, then whole days — borrowing across the actual lengths of each calendar month where needed. That's it; no special magic. If the day-of-month hasn't been reached yet in the current month, one month gets borrowed back into the day-count, and the borrowed days are the real number of days in the previous calendar month — 28 or 29 for February, 30 or 31 for the rest.
The thing not to do is divide your total days alive by 365.25. It looks reasonable, and the answer drifts. Years aren't uniformly 365.25 days, months aren't uniformly 30.4375 days, and the small rounding errors compound. A person whose total days alive / 365.25 says "27.0001" can in fact be 27 years and one day, or 26 years 11 months and 30 days, depending on exactly when in their life the leap days fell.
The leap-day edge case. Someone born February 29 has a calendar birthday only once every four years. They age normally — the year-month-day arithmetic above still works — and on March 1 of a non-leap year, the calculator (and most legal systems) treats them as having just turned a year older. Whether the legal birthday in common years is February 28 or March 1 varies by jurisdiction; we don't pick a side here.
Other ways of counting age
The "chronological" age this calculator computes is the international convention — you're born at age 0 and the counter ticks up on each birthday. It isn't the only way cultures have measured age. Two East Asian systems are worth knowing about, because the question "how old are you?" used to give a different answer in Korea, Japan, China, Vietnam and elsewhere — and in some social contexts still does.
In traditional Korean age, you're 1 at birth and gain a year every January 1, not on your birthday. In counting age, you're 0 at birth but still gain a year every January 1. So a person born in late December becomes 2 by Korean age within their first ten days, and 1 by counting age — the same person who is still 0 by international age.
A worked example, drawn from contemporaneous news reporting: someone born in December 2000 was, in late 2022, 22 by international age, 23 by counting age and 24 by traditional Korean age. South Korea was the last East Asian country still using the traditional system in official contexts; on June 28, 2023, a law passed in December 2022 took effect and standardised the country on international age for judicial and administrative purposes (reported by CNN, BBC and CBS News at the time). The traditional system remains common socially.
What does your age mean statistically?
The U.S. Social Security Administration publishes a period life table each year — a table of average remaining years of life by exact age and sex, computed as if the current year's mortality rates held for life. It's the cleanest population-level answer to "how long is someone my age likely to live for, on average?" — and a population average is precisely what it is, never a personal prediction.
Life expectancy at your age
The life-expectancy curve below comes from the 2023 SSA table. Men's line starts at about 76 average remaining years at birth and women's at about 81; both fall as age advances, but never reach zero — the remaining-years figure stays positive at every age in the table because, demographically, someone is always still expected to live for some non-trivial number of additional years.
How long does the typical American live?
Most people born today live well into their 80s. The 2023 SSA period table tracks 100,000 newborns of each sex through every age. By 50, more than 95,000 of each cohort are still living. By 65, 79,084 American men and 87,399 American women remain.
By around 80, about half the original cohort is still living. The median expected lifespan, the age at which half the original cohort is still alive, is about 80 for men and 85 for women, well above the at-birth life-expectancy quotes of 75.8 and 81.1.
The full milestone series is in the table below. Read down a column to see how each cohort thins through the decades; read across a row to compare men and women at the same age.
| Reach age | Men (out of 100k) | % of cohort | Women (out of 100k) | % of cohort |
|---|---|---|---|---|
| 50 | 91,126 | 91.1% | 95,269 | 95.3% |
| 65 | 79,084 | 79.1% | 87,399 | 87.4% |
| 75 | 62,797 | 62.8% | 75,248 | 75.2% |
| 80 | 50,785 | 50.8% | 64,606 | 64.6% |
| 85 | 35,529 | 35.5% | 49,469 | 49.5% |
| 90 | 19,063 | 19.1% | 30,504 | 30.5% |
| 100 | 999 | 1.0% | 2,758 | 2.8% |
Why expected remaining rises with current age
The at-birth figure of 75.8 years for American men averages in everyone — including infant mortality and the full range of risks across a lifetime. Conditional on having already reached your current age, the average expected lifespan rises.
At 65, the average American man can expect to reach about 83. At 80, the average is closer to 88. The same pattern holds, slightly higher, for women.
This is a survival-selection effect, not a personal forecast. It's the demographic way of saying that the next decade of life, for anyone already at it, is statistically less eventful than the first decade was for the original cohort. The life-expectancy curve falls as the calendar advances, but it falls more slowly than the calendar does — the gap between "expected remaining years" and "years remaining until you'd reach the at-birth figure" widens with every birthday.
Why women outlive men, and the gap that narrows
American women have a longer average lifespan than American men at every age in the 2023 SSA table. The gap is widest at birth — about 5.3 years — and narrows monotonically across the decades. By age 65 the gap is about 2.5 years; by age 90 it's down to roughly 1.3 years. At every age, the women's life-expectancy curve runs above the men's; the chart below subtracts one from the other to show that single gap directly.
The data on its own doesn't explain the gap — it shows it. Demographers cite a mix of biological factors (the X chromosome, hormonal effects on cardiovascular risk), behavioural factors (occupational hazards, smoking and alcohol patterns across cohorts), and risk exposure (homicide, accident, military service) that have all tracked differently for men and women in the cohorts the 2023 period table averages over. None of these is a prediction for any individual.
All figures in this section are population averages on a 2023 mortality basis. They describe cohorts, not individuals.
How many days, hours, minutes have you been alive?
Days, weeks, hours, minutes are direct conversions of total days from your date of birth to the target date. The result card breaks them all out from your calculated age. There is a wrinkle: total days alive depends on how many February 29s your lifetime has covered, so a person two months younger than you can have a noticeably different "days alive" count if a leap day falls between you.
Our day count is midnight-to-midnight (UTC), so it doesn't account for the hour you were actually born, daylight-saving transitions, or your local timezone. Those would change the hour and minute totals at the margin; the day count is correct.
One honest sentence on the dog-years rule: it's a folk heuristic, not a calculation — there's no widely-accepted age-conversion formula, and we don't build one here.