Age Calculator

What this calculator does

Enter your date of birth and a date to calculate against (it defaults to today), and this calculator works out:

• your exact age in years, months, and days
• how many days remain until your next birthday
• the day of the week you were born
• your Western zodiac sign
• life stats: total days, weeks, months, hours, and minutes you've been alive
• a checklist of milestone birthdays (18th, 21st, 25th, 30th, 40th, 50th, 65th, 100th) and milestone day-counts (10,000 and 20,000 days alive), showing whether each has already been reached

Formula Used

The years/months/days breakdown is calculated by finding the largest whole number of calendar months between your date of birth and the target date, then counting the remaining days:

$$totalMonths = (targetYear - birthYear) \times 12 + (targetMonth - birthMonth)$$

That total is adjusted down by one month if adding it to your birth date would overshoot the target date (this keeps short months like February from producing a negative day count). The remainder splits into:

$$years = \left\lfloor \frac{totalMonths}{12} \right\rfloor, \quad months = totalMonths \bmod 12$$

with days being the number of days between the adjusted month-anchor date and the target date.

Total days lived is a straight day count:

$$totalDays = \left\lfloor \frac{targetDate - birthDate}{86400000} \right\rfloor$$

Weeks, months (years × 12 + months), hours (totalDays × 24), and minutes (hours × 60) are all derived from that.

Next birthday

The calculator finds the next occurrence of your birth month/day on or after the target date and reports the number of days remaining.

Zodiac sign

Your Western (tropical) zodiac sign is determined from your birth month and day using the standard date ranges (e.g. Aries: March 21 - April 19).

Example

Someone born on 1995-06-15, checked on 2026-07-09:

• Exact age: 31 years, 0 months, 24 days
• Total days lived: 11,347
• Zodiac sign: Gemini
• Day of week born: Thursday
• Milestones like the 18th, 21st, 25th, and 30th birthdays, plus 10,000 and 20,000 days alive, all show as already reached; later milestones show the number of days remaining.

Notes

• Dates are compared as whole calendar days (no time-of-day or timezone offset is considered).
• If you pick a target date earlier than the date of birth, the calculator will show an error instead of a negative age.
• The zodiac sign shown is the Western tropical zodiac, for fun - not to be confused with Vedic/sidereal systems used elsewhere on this site.