How to use the age calculator
- Choose Exact age or Age difference between two people.
- Enter the date of birth. For exact age you can change the "age on" date from today to any date.
- Read the age in years, months and days, total days and weeks, the weekday of birth and the next birthday.
Formula
Whole months = the most months you can add to the birth date without passing the "age on" date
Years = whole months / 12 (rounded down); remaining months = whole months mod 12
Days = days from that anniversary to the "age on" date
Next birthday = the next date with the same month and day (Feb 29 becomes Feb 28 in common years)
The calculation runs in your browser. Your date of birth is not sent anywhere, and it is not included in share links.
Worked example
Born May 15, 1990. On October 10, 2026: 36 years later is May 15, 2026, 4 more months is September 15, 2026 and 25 more days reaches October 10. The age is 36 years, 4 months, 25 days.
That is 13,297 days, the person was born on a Tuesday, and the next birthday is May 15, 2027, which is 217 days away.
Born February 29, 2000 on February 28, 2026: the age is 26 years because in a common year the birthday is treated as February 28.
Age difference
Choose "Age difference" and enter two dates of birth. The result is the gap between them in years, months and days, found by the same stepping method. It does not matter which person is entered first.
Leap-day birthdays
People born on February 29 have a calendar birthday only every four years. In other years this calculator treats February 28 as the birthday. Legal rules for the exact day an age is reached vary, so check the rule that applies if it matters for a legal purpose.
Age on a specific date
Change the "age on" date to find out how old someone was or will be on a date: the first day of school, an eligibility cutoff or a retirement date. Rules for the exact moment someone reaches an age can vary, so check the specific rule for legal purposes.
Assumptions and limits
- Ages use the Gregorian calendar. Cultural age systems that count differently are not supported.
- A future date of birth is rejected.
- Time of birth and time zones are not used.
Frequently asked questions
How do I calculate my age in days?
The result shows total days from your birth date to the "age on" date. Today is the default.
Is my birth date stored?
No. It is processed in your browser only and never leaves your device.
How is age at a future date calculated?
Change the "age on" date to the future date. The calculator reports how old you will be that day.