How to Calculate Age: Date of Birth to Today Explained

The Basic Age Calculation

Your age is the number of complete years that have passed since your date of birth. To calculate it:

1. Take the current year and subtract your birth year.
2. If your birthday has not yet occurred this year, subtract 1.

Example: Born June 15, 1995. Today is April 4, 2026.
2026 − 1995 = 31. But June 15 hasn't happened yet in 2026, so age = 30 years old.

Calculating Exact Age (Years, Months, Days)

For a more precise age:

1. Years: Full years completed since birth (as above).
2. Months: Full months since the last birthday month.
3. Days: Days since the last monthly anniversary.

Example: Born June 15, 1995. Today: April 4, 2026.
Age = 30 years, 9 months, 20 days.

Calculation: From June 15, 2025 (last birthday) to April 4, 2026 = 9 full months (June 15 → March 15) + 20 days (March 15 → April 4).

Leap Year Considerations

People born on February 29 (a leap day) only have a true birthday once every 4 years. In non-leap years, they typically celebrate on either February 28 or March 1, depending on personal preference and jurisdiction. For legal purposes, most countries treat February 28 as the birthday equivalent in non-leap years.

How Age Is Counted in Different Cultures

Not everyone counts age the same way:

• Western counting: Age starts at 0 at birth; you are "1" after your first birthday.
• East Asian traditional counting (Korea): Babies are considered 1 at birth (counting the time in the womb), and everyone gains a year on New Year's Day rather than on their birthday. South Korea legally standardized to the Western system in 2023.
• Chinese traditional: Similar to Korean — sometimes 2 years different from Western age.

Age Calculation for Legal Purposes

Legal age milestones vary by country. In the US, you're legally an adult at 18. Retirement age is typically 65–67 for full benefits. Driver's license eligibility is often 16–17. When applying for benefits, insurance, or legal documents, your legal age is based on your Western-counted birthday.

Days Since Birth

For a fun fact: multiply your age by 365, add the days since your last birthday, and add leap days (roughly age ÷ 4). At 30 years old, you've been alive for approximately 10,957 days. At 40, about 14,610 days.