How to Use This Age Calculator
Three quick steps. The calculator updates as you type, and every result shows the breakdown so you can verify it at a glance.
What Is an Age Calculator?
A tool that turns two dates into a precise duration — useful far beyond birthdays.
The chronological definition
Chronological age is the number of completed years, months, and days between your date of birth and a reference date (usually today). Most legal systems use this definition for voting, driving, and retirement eligibility.
Why a calculator beats mental math
Calendar math is harder than it looks: months have 28–31 days, leap years add a day every four years (with exceptions), and century boundaries shift weekdays. A calculator removes the arithmetic so you can focus on the answer.
How Age Is Calculated
The math under the hood. Hover any formula for a plain-English explanation.
The year–month–day method
EndYear − StartYear (− 1 if before birthday)EndMonth − StartMonth (borrow if negative)EndDay − StartDay (borrow days from prev month)Leap year handling
A year is a leap year if it's divisible by 4, except century years (1900, 2100) which must also be divisible by 400. People born on February 29 are treated as turning a year older on March 1 in non-leap years — the convention used by most legal systems.
Worked Examples
Three real-world walkthroughs. Expand any example to see the step-by-step math.
Birthday today
Born 15 May 1990, today is 15 May 2026:
36 years, 0 months, 0 days
Show steps →
Before birthday
Born 20 Aug 1985, today is 21 June 2026:
40 years, 10 months, 1 day
Show steps →
Infant in days
Born 1 March 2026, today is 21 June 2026:
0 years, 3 months, 20 days (≈112 days)
Show steps →
Common Use Cases
Beyond curiosity — these are the situations people use an age calculator for most often.
Age in Different Cultures
Not every culture counts age the same way. Two common systems — and where they differ.
Western (international) age
You are 0 at birth and turn 1 on your first birthday. This is the system used by this calculator and by most legal frameworks worldwide, including international travel, sports, and medicine.
East Asian (Korean) age
Traditionally, a baby is considered 1 year old at birth and gains a year on each Lunar New Year — so a December baby can be “2” just weeks after birth. South Korea officially adopted international age in 2023, but cultural usage continues.
Quick Reference Table
Approximate conversions between common age units, useful for a quick sanity check.
| Age | Months | Weeks | Days |
|---|---|---|---|
| 1 year | 12 | ≈ 52 | 365 (or 366) |
| 5 years | 60 | ≈ 261 | ≈ 1,826 |
| 10 years | 120 | ≈ 521 | ≈ 3,652 |
| 18 years | 216 | ≈ 939 | ≈ 6,574 |
| 25 years | 300 | ≈ 1,304 | ≈ 9,131 |
| 50 years | 600 | ≈ 2,608 | ≈ 18,262 |
| 75 years | 900 | ≈ 3,912 | ≈ 27,393 |
| 100 years | 1,200 | ≈ 5,217 | ≈ 36,524 |
Frequently Asked Questions
Quick answers to the questions people ask most about age calculations. Every answer here is mirrored in the page's FAQPage structured data for search engines.