How to use the age calculator
- 1
Enter the date of birth
Pick the day, month and year someone was born.
- 2
Check the “Age on” date
It starts on today. Change it to find an age on a past or future date, such as a school cut-off or retirement date.
- 3
Read the full breakdown
You get age in years, months and days, totals in months, weeks, days and hours, the weekday of birth and the countdown to the next birthday.
How age is worked out
The calculator counts full years first, then full months, then the days left over. That's the same method used on passports, medical records and school forms, so the result matches what an official form expects.
Full months: July 20 → October 20 = 3 months
Remaining days: October 20 → October 21 = 1 day
Age: 36 years, 3 months, 1 day
If the day of the month hasn't been reached yet, you borrow the length of the previous month. That's why ages that span the end of a short month like February can look a day different from a rough “divide by 30” estimate.
Age in months, weeks, days and hours
Exact totals on each birthday, for someone born on January 1, 2000. Leap days make every row slightly different from a simple multiplication.
| Age | Months | Weeks | Days | Hours |
|---|---|---|---|---|
| 1 | 12 | 52 | 366 | 8,784 |
| 5 | 60 | 261 | 1,827 | 43,848 |
| 10 | 120 | 521 | 3,653 | 87,672 |
| 16 | 192 | 834 | 5,844 | 140,256 |
| 18 | 216 | 939 | 6,575 | 157,800 |
| 21 | 252 | 1,095 | 7,671 | 184,104 |
| 25 | 300 | 1,304 | 9,132 | 219,168 |
| 30 | 360 | 1,565 | 10,958 | 262,992 |
| 40 | 480 | 2,087 | 14,610 | 350,640 |
| 50 | 600 | 2,609 | 18,263 | 438,312 |
| 60 | 720 | 3,130 | 21,915 | 525,960 |
| 65 | 780 | 3,391 | 23,742 | 569,808 |
| 70 | 840 | 3,652 | 25,568 | 613,632 |
| 80 | 960 | 4,174 | 29,220 | 701,280 |
| 90 | 1,080 | 4,696 | 32,873 | 788,952 |
| 100 | 1,200 | 5,217 | 36,525 | 876,600 |
Ages that matter in the US and UK
| Milestone | United States | United Kingdom |
|---|---|---|
| Voting | 18 | 18 (16 in Scotland and Wales for some elections) |
| Buying alcohol | 21 | 18 |
| Full driving licence | 16 to 18, varies by state | 17 |
| Early retirement benefits | 62 (Social Security) | — |
| Full pension age | 67 if born 1960 or later | 66, rising to 67 between 2026 and 2028 |
| Medicare / free prescriptions | 65 (Medicare) | 60 in England (free prescriptions) |
Rules change, so confirm with the official government source before relying on a legal age.
Fun facts about your age
| Milestone | When it happens |
|---|---|
| 1,000 days old | About 2 years, 8 months, 26 days |
| 1 billion seconds old | About 31 years, 8 months |
| 10,000 days old | About 27 years, 4 months |
| 500,000 hours old | About 57 years |
| 20,000 days old | About 54 years, 9 months |
| 30,000 days old | About 82 years, 2 months |
Your exact dates depend on your birthday and the leap years you live through. The How Many Days Old Am I tool lists your personal milestone dates.
How age is counted around the world
In the US, UK, Canada and Australia, a baby is 0 at birth and turns 1 on their first birthday. That's the international method, and it's what this calculator uses. Some East Asian traditions counted differently. In traditional Korean age reckoning, a baby was 1 at birth and everyone gained a year on New Year's Day, so someone could be up to two years “older” than their international age. South Korea officially standardised on international age for legal and administrative use in June 2023.
Legal systems also differ on exactly when you reach an age. In most places you turn 18 at the start of your 18th birthday. If you were born on February 29, the law in your country decides whether your birthday is February 28 or March 1 in common years.
Calculating age in Excel and Google Sheets
With the date of birth in cell A1, these formulas give the same parts this calculator shows:
| Result | Formula |
|---|---|
| Full years | =DATEDIF(A1, TODAY(), "y") |
| Months after the last birthday | =DATEDIF(A1, TODAY(), "ym") |
| Days after the last full month | =DATEDIF(A1, TODAY(), "md") |
| Total days | =TODAY()-A1 |
| Age as a decimal | =YEARFRAC(A1, TODAY()) |
Microsoft notes that the “md” option of DATEDIF can give wrong results in some edge cases, especially around the end of a month. This calculator uses its own calendar logic, so it isn't affected.
Common age calculation mistakes
- Subtracting birth year from current year. 2026 − 1990 = 36, but if the birthday hasn't happened yet this year, the person is still 35.
- Dividing days by 365. This ignores leap days and drifts by about a day every four years. After 40 years, it's off by roughly 10 days.
- Using 30-day months. Converting total days to months by dividing by 30 gives a different answer from calendar months, which is what forms ask for.
- Using the wrong reference date. School and sports cut-offs use age on a specific date, not today. Change the “Age on” field to match.
How to describe a baby's or child's age
Doctors and parents usually describe young children's ages in smaller units, switching to larger ones as the child grows. The age calculator gives you every unit at once, so you can use whichever fits.
| Age range | Usually described in | Example |
|---|---|---|
| Birth to 2 weeks | Days | “She's 10 days old” |
| 2 weeks to 3 months | Weeks | “He's 9 weeks old” |
| 3 months to 2 years | Months | “She's 18 months old” |
| 2 to 3 years | Years and months, or months | “He's 2 and a half” or “30 months” |
| 3 years and up | Years | “She's 4” |
For premature babies, doctors often use corrected age, which is the age from the original due date rather than the birth date. To work it out, subtract the number of weeks the baby was born early from their age in weeks.
How old will I be in a future year?
Set the “Age on” field to any future date, such as January 1, 2030 or the day you plan to retire. The calculator shows your exact age on that day. As a quick check, subtract your birth year from the future year: that's the age you'll turn during that year. If your birthday falls later in the year than the date you picked, you'll be one year younger on that date.
On December 1, 2030: the birthday has passed, so the age is 45.
Why people check their exact age
Forms and applications
Passports, insurance and visa forms often ask for age in years and months, or need you to be over a cut-off on a specific date.
School entry
Kindergarten and school admissions use an age on a fixed date, like being 5 by September 1.
Sports and competitions
Age groups are usually set by age on a certain date or at the end of the year.
Retirement planning
Find your exact age on a future date to plan pension and benefit claims.
Leap-day birthdays
About 1 in 1,461 people is born on February 29. In common years, most systems, including this calculator, count February 28 as the birthday. In the UK and some US states, the legal birthday for reaching an age like 18 is March 1. Either way, a leap-day baby still gains a year of age every year.
More age tools
Counting down to the next birthday? Set it up in the Countdown Timer and share the link.