Age calculator
Find an exact age, in years, months and days.
- Total days and weeks lived
- Next birthday countdown
- Age on any chosen date
How to calculate age
- Enter the birth date.
- Optionally pick a date to calculate age on, instead of today.
- Read the exact age and the next birthday.
A worked example
Someone born March 15, 2000 and checked on September 24, 2025 is exactly 25 years, 6 months and 9 days old. That is 9,324 total days lived, which comes out to exactly 1,332 weeks with no remainder.
Why people check age in days or weeks
- Milestone countdowns, like a 10,000th day of life. For someone born March 15, 2000, that lands on August 1, 2027.
- A baby's age in weeks during the first year or two, which pediatric growth charts and vaccine schedules often use instead of months.
- Age-restricted eligibility, like confirming someone will be 18 or 21 by a specific cutoff date rather than by today.
- Milestone anniversaries measured in exact days rather than years, such as a wedding or a sobriety date.
Leap year birthdays
A leap year happens roughly every 4 years, except a century year must also be divisible by 400, so 2000 was a leap year but 1900 was not. Someone born on February 29 only has a real birthday in a leap year; in every other year, this tool counts the next birthday as February 28.
Common exact-age situations, in the US
| Situation | Typical age threshold |
|---|---|
| Learner's permit | Often 15 to 16, varies by state |
| Voting eligibility | 18 |
| Renting a car without a young-driver fee | Often 25 |
| Full Social Security retirement age (born 1960 or later) | 67 |
| Common senior discount age | Often 65 |
These thresholds vary by state, company and country, so use this tool to confirm the exact date someone reaches an age, then check the specific rule that applies.
Age calculator FAQ
What does total days lived mean?
The full number of days between the birth date and the date you are checking, which is useful for milestone countdowns like a 10,000th day.
What happens with a February 29 birthday?
In years without February 29, the next birthday is treated as February 28.
Can I find my age on a future or past date, not just today?
Yes, enter a date in the "age on this date" field to calculate age as of that day instead of today.
Why do I get an error?
The birth date must be on or before the date you are checking against. Check that both dates are entered correctly.
How old is someone born March 15, 2000, on September 24, 2025?
Exactly 25 years, 6 months and 9 days old, having lived 9,324 days, which is exactly 1,332 weeks.
When is someone's 10,000th day of life?
It depends on their birth date, since leap days shift the count slightly. For someone born March 15, 2000, day 10,000 falls on August 1, 2027.
Why do pediatricians talk about a baby's age in weeks?
In the first year or two, weeks show growth and milestones more precisely than months, since a month can be anywhere from 28 to 31 days. Many growth charts and vaccine schedules are built around weeks or specific day counts rather than calendar months.
Roughly how many weeks old is a 6 month old baby?
About 26 weeks. A month averages a little over 30 days, so 6 months works out to around 182 days, or about 26 weeks.