Age Calculator by Date of Birth: How Old Am I?
Age calculator by date of birth: exact age in years, months and days, how old am I today, a birthday calculator countdown, and an age difference calculator.
Every convention this page applies is named in the result rather than assumed. Your numbers stay in this browser.
Results
How to read this: the verdict describes how much room your numbers leave, not a decision or an offer. Change any input to see how much the result moves.
Assumptions and formula
Age is counted forward from the date of birth to the date you choose: whole years first, then whole calendar months, then the days left over. The day before a birthday is still the previous age. For a 29 February birthday, the anniversary in a common year falls on 28 February or 1 March according to the convention you pick, and the result names the one it used.
Every date is computed in UTC, so a daylight-saving change cannot shorten or lengthen a counted day. Months are whole calendar months, found by advancing from the date of birth and clamping to the target month rather than borrowing an averaged 30 days.
Worked example
Someone born on 15 June 1990 is 36 years, 2 months and 24 days old on 8 September 2026. On 14 June 2026, the day before their birthday, they are 35 years, 11 months and 30 days: not yet 36. Someone born on 29 February 2000 is still 25 on 28 February 2026 under the 1 March convention, and already 26 under the 28 February convention.
Ages in months, weeks, days and hours
Whole years converted to other units, using the average length of a calendar year (365.2425 days, which accounts for leap years). Your exact figure depends on your birth date and how many 29 Februaries you have lived through, which the calculator counts precisely.
| Years | Months | Weeks | Days | Hours |
|---|---|---|---|---|
| 1 | 12 | 52 | 365 | 8,766 |
| 5 | 60 | 261 | 1,826 | 43,829 |
| 10 | 120 | 522 | 3,652 | 87,658 |
| 18 | 216 | 939 | 6,574 | 157,785 |
| 21 | 252 | 1,096 | 7,670 | 184,082 |
| 30 | 360 | 1,565 | 10,957 | 262,975 |
| 40 | 480 | 2,087 | 14,610 | 350,633 |
| 50 | 600 | 2,609 | 18,262 | 438,291 |
| 65 | 780 | 3,392 | 23,741 | 569,778 |
Age is normally counted in completed years: you turn a year older on your birthday, not partway through. Someone born on 29 February is legally treated in most countries as turning a year older on 28 February or 1 March in non-leap years; the rule varies by country.
Some countries have traditionally counted age differently. South Korea, for example, used a system in which a baby is one year old at birth, until it adopted the international method for official purposes in 2023.
Common mistakes to avoid
- Subtracting birth years only. Someone born in December 2000 is 25 in most of 2026, not 26, until their birthday.
- Forgetting leap years when counting days. Every 29 February adds a day to an exact age in days.
- Assuming every country counts age the same way for legal purposes, such as when a birthday on 29 February is recognised.
Frequently asked questions
How does an age calculator by date of birth work out how old I am?
Subtract the birth date from today’s date one unit at a time: years first, then months, then days, borrowing from the previous unit when the day or month has not yet come round this year. Someone born on 15 August 1990 is 36 years, 1 month and 1 day old on 16 September 2026, because September’s 16th comes after August’s 15th; a day earlier they would still be 35 for the last time. Leap-day birthdays count 28 February or 1 March in non-leap years depending on the convention used, and this calculator states which one it applied. The same page answers how old am I today, works as a birthday calculator for the next one, an age calculator by date of birth for anyone else, and an age difference calculator between two people. Set "Age at this date" to the day of a test and it is also a chronological age calculator: school and developmental assessments are scored against age in years, months and days on the testing date. That exact figure, in calendar years, months and days since birth, is your chronological age, so the page also works as a chronological age calculator for today or any other date. It also works as a birth date calculator and an age date calculator: enter a date of birth and any other date to get the exact age on that date. It calculates age from a date of birth to any date, in years, months and days, and when the next birthday falls.
When do I reach Social Security full retirement age?
It depends on the year you were born and it is not 67 for everyone: 66 for those born 1943-1954, stepping up two months per birth year to 67 for 1960 onward. This page derives your own figure from your birth year and gives the date, alongside the RMD age, which has three cohorts under SECURE 2.0. It works as an online age calculation for anyone: enter a date of birth to calculate your age online in years, months and days.