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Simple Calculators

Age Calculator

Your exact age in years, months, and days — plus totals and your next birthday countdown

Dates

Defaults to today

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Quick summary

Enter your date of birth to get your exact calendar age in years, months, and days, plus your age in total months, weeks, days, and hours, the day of the week you were born, and a countdown to your next birthday. Change the Age As Of date to find your age on any past or future date — useful for forms, eligibility cutoffs, and milestones.

Reviewed by Simple Calculators TeamLast reviewed

How to use this calculator

  1. Enter your birthday in the Date of Birth field.
  2. Leave Age As Of set to today, or change it to the date you need your age on — for example, a school cutoff or an application deadline.
  3. Read Your Age at the top of the results: full years, then months, then days.
  4. Check the totals row for your age in Total Months, Total Weeks, Total Days, and Total Hours.
  5. Use the Details card for the Day of the Week You Were Born and the Days Until Next Birthday, or press Reset to start over.

Age Calculation Formulas

Exact Calendar Age

Age=(Ya−Yb) y+(Ma−Mb) m+(Da−Db) d\text{Age} = (Y_a - Y_b)\,\text{y} + (M_a - M_b)\,\text{m} + (D_a - D_b)\,\text{d}
Y_a, M_a, D_a
Year, month, and day of the Age As Of date
Y_b, M_b, D_b
Year, month, and day of the Date of Birth
Borrow
If days < 0: subtract 1 month and add the days in the month before the as-of date. If months < 0: subtract 1 year and add 12 months.

Worked example

Born June 15, 1990; age as of July 11, 2026

Given
Date of Birth = 1990-06-15
Age As Of = 2026-07-11
Calculation
(2026−1990) y+(7−6) m+(11−15) d⇒36 y+0 m+(−4+30) d(2026 - 1990)\,\text{y} + (7 - 6)\,\text{m} + (11 - 15)\,\text{d} \Rightarrow 36\,\text{y} + 0\,\text{m} + (-4 + 30)\,\text{d}
Result
36 years, 0 months, 26 days (June has 30 days, so 1 month is borrowed as 30 days)

Age in Days and Weeks

Total Days=As-of date−Birth date,Total Weeks=⌊Total Days7⌋\text{Total Days} = \text{As-of date} - \text{Birth date}, \quad \text{Total Weeks} = \left\lfloor \frac{\text{Total Days}}{7} \right\rfloor
Total Days
Exact calendar days between the two dates, leap days included
Total Weeks
Complete weeks in that span (rounded down)

Worked example

Same dates: born June 15, 1990; as of July 11, 2026

Given
Date of Birth = 1990-06-15
Age As Of = 2026-07-11
Calculation
Total Weeks=⌊13,1757⌋=1,882\text{Total Weeks} = \left\lfloor \frac{13{,}175}{7} \right\rfloor = 1{,}882
Result
13,175 days = 1,882 complete weeks (316,200 hours)

Frequently asked questions

How is exact age calculated?

Exact age is counted in calendar units: full years first, then full months, then the leftover days. If the day count is negative, the calculator borrows the days of the previous month; if the month count is negative, it borrows 12 months. Someone born June 15, 1990 is 36 years, 0 months, 26 days old on July 11, 2026. You turn a new age on your birthday, not after fixed 365-day blocks.

How many days old am I?

Your age in days is the exact number of calendar days between your birth date and the Age As Of date, leap days included — the calculator shows it as Total Days. For example, someone born June 15, 1990 is 13,175 days old on July 11, 2026. For a rough estimate, multiply your age in years by 365.25.

How do I calculate my age on a specific date?

Set the Age As Of field to that date instead of today. The calculator then reports your age in years, months, and days on that exact date, along with the totals. This is handy for age-based cutoffs such as school enrollment, sports divisions, insurance, or retirement plans, which often ask how old you will be on a particular day.

What if I was born on February 29?

In non-leap years, this calculator treats March 1 as your birthday. For someone born February 29, 2000, it shows 24 years, 11 months, 30 days on February 28, 2025, and exactly 25 years on March 1, 2025. Laws and organizations differ on whether February 28 or March 1 counts, so check the rule that applies to you.

What day of the week was I born?

The calculator shows it in the Details card as the Day of the Week You Were Born, worked out from the calendar for your birth date. For example, June 15, 1990 was a Friday. It also tells you which weekday your next birthday falls on, which is useful for planning a celebration.

How many days until my next birthday?

The Days Until Next Birthday figure counts from the Age As Of date to your next birthday. If your birthday is on that date, the countdown rolls to the following year. For example, someone born June 15 who checks on July 11, 2026 has 339 days to go, and that birthday falls on a Tuesday.

When is age calculated differently?

Some systems do not use the Western calendar-age convention this calculator follows. Traditional East Asian age reckoning counted a newborn as one year old, many racing and breeding registries give horses a shared birthday, and schools often use age as of a fixed cutoff date. For a cutoff date, set Age As Of to that date.

Key terms

Chronological Age
Time elapsed since birth — the standard age used on forms and IDs.
Calendar Age Method
Counting full years, then months, then days — rather than dividing total days by 365.25.
Leap Year
A 366-day year (every 4 years, except century years not divisible by 400) — why exact day counts differ from ×365.

Methodology, sources & limitations

This page shows the formula, assumptions, and limitations used for this estimate. Rates, thresholds, and other time-sensitive inputs can change, so verify them against the relevant official source before relying on a result.

For our review approach and the primary sources we consult, see the methodology and source policy. If you spot an outdated figure or formula, please contact us with a correction.