To calculate age, subtract the birth date from the current date. This gives the duration in years, months, and days. The easiest method is to use our Age Calculator, which does this automatically.
Manual age calculation
To calculate your age manually, start with the current year minus your birth year. Then check whether your birthday has already occurred this year. If it has, that's your age. If it hasn't, subtract 1. For example, if you were born on August 15, 1990, and today is July 12, 2026: 2026 - 1990 = 36, but since August 15 hasn't happened yet, you're still 35.
Why exact age matters
For most purposes, knowing your age in years is sufficient. But for legal documents, medical forms, insurance applications, and milestone tracking, exact age in years, months, and days is often required. Infant developmental milestones are tracked by months (not years). Legal age thresholds (18, 21, 65) are determined by the exact date, not the calendar year.
How the calculator handles edge cases
The Age Calculator accounts for leap years (February 29 birthdays are handled correctly), varying month lengths (31, 30, 29, or 28 days), and timezone differences (the calculation uses your local date). It also prevents you from entering a future birth date, which would produce a negative age.