Age Calculator
Need your exact age in years, months and days? Enter your birth date and you will see it instantly, leap years included. It is handy for forms, anniversaries, and planning ahead.
TL;DR
- The calendar has months of different lengths and a leap day every four years
- Conceptual Calculation Logic: Age = Reference Year - Birth Year (Adjusted by Month & Day of current year)
- Example 1: Born on October 15, 1990, reference is June 10, 2026
How it works
The calendar has months of different lengths and a leap day every four years. A good calculator counts those variations instead of using a fixed 365 days.
The math
Subtract birth year from the reference year. If your birthday has not happened yet this year, subtract one more year.
Subtract birth year from reference year. If the current month and day are chronologically before the birth month and day, subtract 1 from the calculated years.
Examples
Example 1: Born on October 15, 1990, reference is June 10, 2026
- Difference in years: 2026 - 1990 = 36 years
- Compare month of birth (10) to current month (6)
- Since 6 < 10, the birthday has not been reached yet in 2026
- Adjust age: 36 - 1 = 35 years old
Example 2: Born on Feb 29, 2000, reference is Feb 28, 2025
- 2000 was a leap year; 2025 is a non-leap year
- Since Feb 29 does not exist in 2025, the legal age increments on March 1st or February 28th depending on jurisdiction.
When to use it
✦ Retirement and Pension Planning
Exact date compliance to file for social security, pension, and life insurance benefits.
✦ Legal Eligibility Requirements
Verifying exact day status for driver licenses, voter registration, and age-restricted access.
✦ School and Kindergarten Enrollment
Verifying if a child meets school entry criteria based on precise birth date cut-off regulations.
⚠ Common mistakes
- Assuming a static 30-day month: Calculating months by simply dividing total days by 30 leads to errors due to February's unique length and 31-day months.
- Leap Year Omission: Neglecting to check for February 29th leads to a cumulative error over multiple decades.
FAQ (6)
How many days are in a leap year?
A leap year has 366 days, adding February 29th to adjust for the Earth's orbit.
What is my age in total days?
Multiply your age in years by 365.2425 and add the remaining days from your last birthday.
What happens to my weight, height or other health data?
It never leaves your phone. BMI, BMR, body-fat — all computed on-device, no upload, no account. That's intentional for health data: you can check a BMI of 22.8 or a TDEE of 2,100 kcal without worrying about a server log. Closing the tab clears the form from memory.
Does it work offline at the gym or on a plane?
Yep. Once the page has loaded, the calculators are fully offline-first. I've used the pace and BMI tools in airplane mode between flights — no spinner, no retry, just instant numbers. Same for sleep cycles if you're planning a shift.
Can my doctor rely on these numbers?
They're solid estimates using published formulas (WHO for BMI, Mifflin-St Jeor for BMR, CKD-EPI for GFR) but they're not a diagnosis. Think of them as a conversation starter: good for tracking trends, but your GP or nephrologist should interpret GFR, heart age or pregnancy dates with labs and context. We link the sources at the bottom for that reason.
How can I share my result with a trainer or doctor?
Use 'Share Link' in the results panel. It builds a URL with your inputs — for example BMI 70kg/175cm — so they see exactly what you entered. No data is stored on our side, the link just carries the numbers.