U.S. Naval Observatory leap year rules
Used for Gregorian leap-year handling, including century-year exceptions that affect exact date arithmetic.
View USNO leap year rules
Exact Age
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Enter valid dates to calculate age.
Total Months
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Total Weeks
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Total Days
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Total Hours
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Total Minutes
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Total Seconds
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Insights
Next Birthday Insights
See practical date insights beyond the core age output.
Day of Week Born
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Next Birthday
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Days Until Birthday
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Half Birthday
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Common Questions
Age Calculator FAQ
Quick answers for exact age rules, leap-day handling, and reverse DOB workflows.
1. How is exact age calculated?
Exact age is calculated in full calendar years, then full months, then remaining days between the two dates.
2. How old was I on a specific date?
Use Age on Date, set your DOB and target date, and the tool returns exact age on that day.
3. Can I calculate date difference without DOB?
Yes. Use Date Difference to compare any two dates for years, months, days, and total elapsed units.
4. Can I find date of birth from age?
Yes. Use Reverse Age / DOB with years, months, days, and an as-of date to estimate DOB.
5. How are Feb 29 birthdays handled?
The calculator lets you choose a non-leap-year rule: treat birthday as Feb 28 or Mar 1.
6. Why can month-end outputs look unusual?
Calendar months have different lengths. Exact calendar logic can produce results that differ from average-day approximations.
Data Integrity
Methodology and source verification
The date math on this page is cross-checked against Gregorian calendar rules, leap-year handling, and completed calendar-year or month difference logic used for exact age calculations. The calculator measures elapsed time between dates, but it does not verify legal identity, official age status, or jurisdiction-specific interpretations of age-based deadlines.
Verified
Reference basis: the calculation engine compares full calendar dates, accounts for variable month lengths, and applies Gregorian leap-year rules when deriving exact age, date difference, and reverse DOB outputs. The explanatory copy is anchored to civil-calendar references and federal data standards that describe age as a date-derived value.
U.S. Naval Observatory calendar introduction
Used for the Gregorian calendar baseline that underpins month-length and date-to-date calculations.
Read USNO calendar overviewNIST leap year explanation
Used to validate the civil-calendar treatment of leap years and the practical handling of February 29 dates.
Read the NIST leap-day explanationNIH FITBIR age-derived value
Used for the principle that age is derived from the difference between an event date and a birth date, not stored as independent calendar logic.
View NIH age-derived standard