Age Calculator
Calculate exact chronological age in calendar years, months, and days, total elapsed days, and countdown to next birthday.
How It Works & Methodology
Calculating true chronological age requires calendar date arithmetic rather than dividing elapsed days by 365 or 365.25, because month lengths vary between 28 and 31 days and leap years introduce extra days.
Calendar age counts completed full calendar years, remaining completed calendar months, and remaining days.
For February 29 leap-day birthdays, common non-leap years celebrate the birthday on February 28.
Key Assumptions & Scope:
- Inputs follow standard ISO-8601 calendar dates (YYYY-MM-DD).
- Calculation uses pure Gregorian UTC calendar math, eliminating local Daylight Saving Time (DST) hour-shifts.
- The "as of" comparison date must be identical to or later than the birth date.
Frequently Asked Questions
Why not simply divide total days by 365.25?
Dividing by 365.25 produces fractional approximations. Calendar age depends on the exact calendar distribution of leap years and specific month lengths.
How are leap day (Feb 29) birthdays handled?
In common non-leap years containing only 28 days in February, the anniversary is computed as February 28 per standard civil conventions.
Can I calculate an age at a specific past or future date?
Yes. You can customize the "As of Date" field to determine how old someone was or will be at any milestone date.