Age Conversion Calculator
Age conversion calculator works out Age in years and Extra months from Date of birth and Age at this date. The default figures on this page give days lived of 12,523 days; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
6 steps
- Born 1990-06-15 (a Friday); measuring on 2024-09-27.
- Whole years first: 1990-06-15 + 34 years lands on or before 2024-09-27.
- Then whole months and days: + 3 month(s) + 12 day(s) reaches 2024-09-27.
- Elapsed days = 12,523, i.e. 1789 weeks and 0 day(s).
- Next birthday 2025-06-15 (Sunday), 261 day(s) away; turning 35.
- Same age in every unit: Years: 34; Months: 411; Weeks: 1,789; Days: 12,523; Hours: 300,552; Minutes: 18,033,120; Seconds: 1,081,987,200.
The same age in every unittable
Its 9 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
5 sources
What the age conversion calculator calculates
Age in completed years, months and days on any date, with the total days lived, the weekday of birth, the next birthday and the gap between two birth dates; it also runs backwards to recover a date of birth from an age, breaks an age down into every time unit, and corrects an infant age for prematurity. Age counts completed calendar months and days, so a 29 February birth attains the next year of age on 1 March in common years.
How to use this age conversion calculator
Enter Date of birth and Age at this date. Age in years updates as you type. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Age in years, Extra months and Extra days.
The method follows ISO 8601-1:2019, Date and time - Representations for information interchange, Howard Hinnant, chrono-Compatible Low-Level Date Algorithms, US Social Security Administration, Program Operations Manual System GN 00302.400 (age computation), Squires J. and Bricker D., Ages & Stages Questionnaires, Third Edition (ASQ-3) User’s Guide, Brookes Publishing and American College of Obstetricians and Gynecologists, Committee Opinion 700: Methods for Estimating the Due Date.
What you can compare
Change one input at a time to see how it affects Age in years, Extra months and Extra days. The inputs you can vary are Date of birth and Age at this date.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
What is my exact age calculator?
The age conversion calculator follows the stated method, but the result is only as reliable as Date of birth and Age at this date and the assumptions shown. Check the working and sources before relying on it for an important decision.
How do I convert an age in months to years?
Age in completed years, months and days on any date, with the total days lived, the weekday of birth, the next birthday and the gap between two birth dates. Open “How this is worked out” beside the result to see each step for your own figures.
How to convert birthday to age?
It needs Date of birth and Age at this date. Nothing else is required, and the figures stay in your browser.
How do you calculate age in mm, dd, yyyy?
The result gives Age in years, Extra months, Extra days, Age, Chronological age (years;months) and Age in decimal years, each labelled with its unit so the figure can be read on its own.
What information do I need for the age conversion calculator?
You need Date of birth and Age at this date. The page opens with default figures that give days lived of 12,523 days, so you can see the scale before entering your own.
What does this age conversion calculator show?
It shows Age in years, Extra months, Extra days, Age, Chronological age (years;months), Age in decimal years, Age in months and Age in weeks, with the working and any warnings for your entries.