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Age isn't just "years since birth" — the exact number of years, months and days between two dates depends on calendar quirks (different month lengths, leap years) that are easy to get slightly wrong doing the arithmetic by hand. This calculator takes a birth date and, optionally, a specific "as of" date, and works out the exact age down to the day, along with total days and weeks lived, and how many days remain until the next birthday.
By default it calculates age as of today, but setting a specific "as of" date is useful for figuring out someone's exact age on a past or future date — a contract signing date, an eligibility cutoff, or an event date.
How it works
Enter a birth date, and optionally a different "as of" date (it defaults to today if left blank). The calculator works out the exact age in complete years, months and days as of that date, the total number of days and weeks lived, which day of the week the birth date fell on, and how many days remain until the next birthday.
- Enter a birth date.
- Optionally set an "as of" date (defaults to today).
- Click Calculate to see the exact age and related facts.
Examples
Calculating current age
Someone born on June 15, 1990, checking their age as of today, sees their exact age in years, months and days, plus a running total of days lived — often a surprisingly large number.
Checking age eligibility on a specific date
A program requires applicants to be at least 18 on the application deadline. Entering the applicant's birth date with the deadline as the "as of" date gives an exact age on that specific day, not just today.
Who should use it
- Checking someone's exact age as of today or a specific date.
- Verifying age eligibility for a program, contract or legal requirement as of a cutoff date.
- Finding out how many days until a birthday for planning purposes.
- Milestone tracking (e.g. a "10,000 days old" celebration).
Industry applications
- Education and student records
- HR and eligibility verification
- Legal and compliance date calculations
- Event and milestone planning
Advantages
- Calculates exact age in years, months and days, not just whole years.
- Supports calculating age as of any specific date, not only today.
- Includes total days/weeks lived and days until the next birthday as extra, genuinely useful figures.
Limitations
- Does not account for time zone differences if birth time (not just date) matters.
- Age calculations near February 29 in non-leap years follow standard date rollover behavior rather than special-casing leap birthdays.
Common mistakes to avoid
- Calculating age as a simple subtraction of birth year from current year, which is wrong before the birthday has occurred that year.
- Forgetting that "age" for eligibility purposes usually means age as of a specific cutoff date, not today.
- Manually counting days/weeks lived instead of using an exact calendar-based calculation, which is error-prone over long spans.
Best practices
- When age matters for eligibility (contracts, programs, legal requirements), calculate it as of the actual relevant date, not today's date.
- Double check the birth date was entered correctly before relying on an age calculation for anything official.
Tips
- For eligibility checks, always set the "as of" date to the actual cutoff date rather than checking today and assuming it still applies later.
- Use the total-days figure if you need a precise, single-number comparison between two people's ages rather than comparing years/months/days separately.