How this age calculator works
Enter a date of birth and an "age at date" (it defaults to today) to find out exactly how old someone is, or how old they'll be on a future date. This is the same question as "how old am I", just for any two dates you choose.
The calculator first finds the age in whole years and months by comparing calendar dates, then expresses the remaining days as weeks and days. It also reports the same span as a total number of months, weeks, and days, which is useful for things like infant ages or precise date-of-birth calculations.
What the result includes
- Age: years, months, weeks, and days since the date of birth.
- Age in months, age in weeks, and age in days: the same span expressed as a single total unit (plus a smaller remainder).
Calendar math accounts for different month lengths and leap years, so results stay accurate for any date range.
Frequently asked questions
How do I calculate my exact age?
Enter your date of birth and leave "age at date" set to today. The calculator subtracts your birth date from today's date to show your exact age in years, months, weeks, and days.
How many days old am I, or will I be on a certain date?
The "Age in days" result gives a precise day count between the two dates. Change "age at date" to any past or future date to see the day count on that date instead of today.
Why do my age in years and age in months not line up with a simple multiplication?
Months have different lengths (28 to 31 days), so "age in months" is based on actual calendar months elapsed, not a flat 30-day average. That's why years × 12 + months can look slightly different from dividing total days by 30.
Does this account for leap years?
Yes. All totals are computed from real calendar dates, so leap days (February 29) are automatically included in the day, week, and month counts.
What's changed
- Launched.
References
- U.S. Naval Observatory — Calendars and Leap Year Rules
the Gregorian leap year rule: every year divisible by 4 is a leap year, except century years, which must also be divisible by 400