An age calculator counts the completed years since a date of birth, plus the months and days since the last birthday. Someone born on March 15, 2000 is 26 years, 7 months and 5 days old on October 20, 2026, and has lived 9,715 days.
On this page
How to use the age calculator
- Enter the date of birth.
- Read the age in years, months and days as of today’s date on your device.
- Check the total days lived.
The age calculator uses real calendar dates, so leap days and different month lengths are counted.
Age calculation method
- Years: subtract the birth year from the current year, then subtract 1 if this year’s birthday has not happened yet.
- Months: count the full months since the last birthday.
- Days: count the days since the last completed month.
- Total days: the number of calendar days between the two dates.
Example: from March 15, 2000 to October 20, 2026. The 26th birthday was March 15, 2026. From then to October 15 is 7 months, and October 15 to 20 is 5 days.
Age in other units
For the example above:
| Unit | Age |
|---|---|
| Years, months, days | 26 years, 7 months, 5 days |
| Total months | 319 months |
| Total weeks | 1,387 weeks and 6 days |
| Total days | 9,715 days |
Leap-year birthdays
People born on February 29 have a calendar birthday only in leap years. For legal purposes, many places treat March 1 (and some treat February 28) as the birthday in other years, depending on local law.
Age in Excel or Google Sheets
| Result | Formula (birth date in A2) |
|---|---|
| Completed years | =DATEDIF(A2, TODAY(), “Y”) |
| Months after last birthday | =DATEDIF(A2, TODAY(), “YM”) |
| Days after last month | =DATEDIF(A2, TODAY(), “MD”) |
| Total days | =TODAY()-A2 |
Microsoft notes that the “MD” option of DATEDIF can give inaccurate results in some cases, so check edge cases by hand.
Different ways of counting age
Some cultures have traditionally counted a newborn as one year old, or added a year at the new year. South Korea officially standardized on the international “completed years” method in 2023. The age calculator uses completed years.
How months and days are counted
When today’s day of the month is earlier than the birth day, the age calculator borrows a month. For someone born on June 25, 2010, on October 20, 2026: the 16th birthday has passed, October minus June is 4 months, but the 20th is before the 25th, so it is 3 full months. The days are 20 + (30 − 25) = 25, using the 30 days of September. The result is 16 years, 3 months and 25 days, or 5,961 days in total.
Age on forms and official documents
Forms usually ask for age in completed years on a stated date, not today. This age calculator measures to today. To find age on a past or future date, use the date difference calculator with that date as the end date. A person born on December 5, 1990 is 35 years, 10 months and 15 days old on October 20, 2026. Eligibility rules such as school entry or retirement benefits often set a cutoff date; check the exact rule, because being one day short of a birthday still counts as the younger age.
Age on a cutoff date
Schools, sports leagues and some benefit programs ask for age on a specific date rather than today. The age calculator handles this when you set the end date to the cutoff. A child born on 2 September 2021 is 4 years, 11 months and 30 days old on 1 September 2026, so a program that requires age 5 by 1 September would not admit them that year, even though they turn 5 the next day.
Insurance and retirement rules can use different conventions. Some insurers use age at nearest birthday, so a person who is 44 years and 7 months old is rated as 45. U.S. Social Security treats you as reaching an age on the day before your birthday, which matters for anyone born on the 1st or 2nd of a month. If a form or rule does not say which method it uses, ask, and use the age calculator to check each version.
Related converters and calculators
Related tools:
- Date difference calculator: between any two dates
- Day of the week calculator: weekday of a date
- Time duration calculator: hours and minutes
- Social Security break-even calculator: claiming age
Sources
How old am I?
Your age in whole years is the number of birthdays you have already reached as of today. Enter your date of birth in the calculator above. If the birth date is still in the future, Calcenzo shows an error instead of a negative age.
Child age in months and weeks
For infants and toddlers, caregivers often want months and weeks as well as years. After you calculate, read the years, months, and days breakdown in the result detail. Approximate weeks = total days ÷ 7. Pediatric schedules sometimes use completed weeks of life; this tool uses calendar date math, not a clinical gestational age model.
Questions about this calculator
How do I calculate my exact age?
Count the completed years since your birth date, then the full months since your last birthday, then the remaining days.
How old am I in days?
Subtract your birth date from today. Someone born March 15, 2000 is 9,715 days old on October 20, 2026.
How do I calculate age in Excel?
Use =DATEDIF(A2, TODAY(), "Y") for completed years, with the birth date in A2.
Does the age calculator count leap years?
Yes. It uses real calendar dates.
When is the birthday of someone born on February 29?
In non-leap years many places use March 1 and some use February 28, depending on local law.
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
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