Age Calculator
Enter your date of birth and get your exact age in years, months, and days — plus total days and weeks. Works for any two dates, not just birthdays.
Calculator
Years Old
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How Age Calculator Works
How Does the Age Calculator Work?
Our Age Calculator computes the precise interval between two dates — usually a date of birth and today. It breaks the result down into the three components most useful for everyday understanding: complete years, remaining months, and remaining days.
The underlying arithmetic follows the standard calendar convention used worldwide: a full year passes when the same month and day recur in a later year; a full month passes when the same day-of-month recurs in the next month. Remaining days are the gap between the last completed month-boundary and the target date.
Calendar Arithmetic and Month Boundaries
Date arithmetic is more subtle than it first appears because months have different lengths. The general rules are:
- Years: Subtract the birth year from the target year. Subtract one if the birth month-and-day has not yet occurred in the target year.
- Months: Count complete months elapsed since the most recent birthday. Subtract one month if the target day-of-month is earlier than the birth day-of-month.
- Days: Count days elapsed since the most recent month-anniversary. When borrowing a month, use the actual number of days in that month.
Example: Someone born on 31 January whose target date is 1 March is said to be 1 month and 1 day old — not 0 months and 29 days — because one full month (January 31 to February 28) has elapsed, plus one additional day.
Leap Years and February 29
The Gregorian calendar inserts a leap day (29 February) every four years, with century exceptions. This affects age calculations in two ways:
- Counting total days: The calculator always counts the exact number of calendar days between the two dates, accounting correctly for all leap days that fall within the range.
- February 29 birthdays: In years without a leap day, those born on 29 February conventionally celebrate their birthday on 28 February. The calculator follows this convention: a person born on 29 February 2000 turns 25 on 28 February 2025.
A leap year occurs if the year is divisible by 4, except for century years (e.g., 1900), which must be divisible by 400 (e.g., 2000). The year 2024 is a leap year; 2100 will not be.
Total Days and Total Weeks
In addition to the years/months/days breakdown, the calculator reports:
- Total days: The exact count of calendar days between the two dates. Useful for legal and financial contexts where age is measured in days (e.g., bond maturity, neonatal assessments).
- Total weeks: The number of complete seven-day weeks. Useful for pregnancy tracking, fitness programmes, and weekly milestone calendars.
Worked Examples
Example 1 — Standard age: Born 15 March 1990, target date 2 July 2026. Years = 36, months = 3, days = 17. Total days = 13,262. Total weeks = 1,894.
Example 2 — Month boundary: Born 31 January 2000, target date 1 March 2026. Result = 26 years, 1 month, 1 day. (January 31 + 1 month = February 28; February 28 + 1 day = March 1.)
Example 3 — Same date: Born 2 July 2001, target date 2 July 2026. Result = 25 years, 0 months, 0 days. Total days = 9,131.
Example 4 — Date range (not a birthday): Start date 1 January 2024, end date 1 January 2026. Result = 2 years, 0 months, 0 days. Total days = 731 (one leap year in 2024).
Accuracy & Sources
Last reviewed: July 2026. Formula source: Gregorian Calendar Standard. All calculations run in your browser. No data is sent to any server.
Frequently Asked Questions
The calculator is exact to the day. It counts the precise number of calendar days between the two dates, correctly accounting for all leap days within the range. The years/months/days breakdown uses the standard calendar convention: a full year passes when the same month and day recur in a later year; a full month passes when the same day-of-month recurs in the next month. There is no rounding or approximation.
Yes. The 'Calculate to' field defaults to today but accepts any date. Enter a past date to calculate the interval between two historical events, or a future date to count down to an anniversary, deadline, or milestone. The start date must be on or before the end date.
People born on 29 February conventionally celebrate their birthday on 28 February in years without a leap day. Our calculator follows this convention: a person born on 29 February 2000 is considered to turn 25 on 28 February 2025, not on 1 March. The total-days count is always exact regardless of the birthday convention.
Month boundaries are genuinely ambiguous when the birth day does not exist in every month. For example, someone born on 31 January — 31 days do not exist in February. The standard convention, which this calculator uses, is to count one full month from 31 January to 28 February (the last day of February), then continue counting days from there. This matches how most governments, insurers, and legal systems compute age.
Most countries use the Western convention: age increases by one on each anniversary of the birth date. South Korea historically used a system where everyone adds one year at the start of the calendar year, making newborns one year old at birth. As of 2023, South Korea has standardised on the international (Western) convention for official and legal purposes. This calculator uses the Western convention.
Age in years is the count of complete twelve-month periods elapsed since birth — the number most people think of as their age. Age in days (total days) is the exact count of calendar days elapsed, including all partial years. For a 25-year-old born on 2 July 2001, the total days on 2 July 2026 would be exactly 9,131 days (accounting for six leap years in that period). Total days is used in legal, medical, and financial contexts where annual approximations are insufficient.
Enter any start date in 'Date of Birth' and any end date in 'Calculate to'. The result shows the precise interval between the two dates in years, months, and days, plus the total day count and total weeks. This works for any two dates — historical events, project durations, countdowns, or anniversary tracking.
Enter your date of birth and leave 'Calculate to' blank. The calculator will compute your age as of today and display the total days in the result. For example, a person born on 1 January 2000 would be 9,679 days old on 2 July 2026. The exact number changes daily — your age in days is always today's date minus your birth date.