About AgeCalc

AgeCalculators.io is a set of chronological age tools built around one specific job: producing an age in the exact format a form, report or norm table asks for. Most age calculators answer “how old am I”. This one answers “what do I write in the age box” — which is a narrower question with a much less forgiving right answer.

The primary audience is people who calculate ages for a living: school psychologists, speech-language pathologists, early-intervention and special-education evaluators, occupational and physical therapists, and the paediatric and neonatal teams who work with corrected age. The everyday calculators — birthdays, age gaps, dog and cat years — exist because the same date arithmetic answers those questions too, not because they are what the site is for.

AgeCalc is an independent, self-funded project run by a software developer, not by an assessment publisher, a clinic or a university. It is not affiliated with, endorsed by or sponsored by Pearson, Curriculum Associates, PRO-ED, WPS, Riverside Insights, Brookes Publishing, MHS or any other publisher named on this site. Instrument names are used descriptively, to identify the age formats the tools support.

No clinician is credited as a reviewer on these pages, because none has reviewed them. Saying otherwise would be the easiest thing on the internet to fake and the least useful thing to read, so instead the site tells you exactly where each number comes from and gives you the means to check it. If you are a credentialed evaluator willing to review this material under your own name, get in touch — the byline is available.

Every figure on the site comes from one of three places:

• Date arithmetic. Complete years, complete months, then the leftover days, with month-end clamping and leap-day handling spelled out in the calculation methodology. The conventions are stated before the results, so a result that contradicts them is a bug rather than a judgement call.
• Published recording conventions. The years;months.days format, the truncation rule used by most norm tables, and the 15-day nearest-month rounding rule used by BRIGANCE screening are all documented conventions, not house style. Where a convention is instrument-specific it is stated on that instrument's page rather than applied everywhere.
• Publisher-stated metadata. The age ranges in the instrument reference are the ranges the publisher states for that named edition, collected so you can check one without opening five manuals. They are a cross-check, not an authority — publishers revise ranges, norms and rounding rules between editions, and the manual in front of you wins.

The calculation library is covered by an automated test suite that runs on every change. The tests are written from the documented conventions rather than from the code's current output, so they catch a regression instead of blessing one. They cover month-end clamping, leap-day birthdays, the years;months.days string, nearest-month rounding on both sides of the 15-day threshold and across the year boundary, the prematurity adjustment, corrected and postmenstrual age, and the degenerate cases — same-day, future-dated and reversed inputs.

Worked examples printed on the calculator pages are computed by that same library at build time, which means the example on the page and the answer from the tool cannot drift apart. If you want to check a result by hand, the printable worksheet sets out the manual borrow method step by step.

The conventions on the methodology page are the contract. If a result contradicts them, or if a published age range or format note here is wrong, that is a defect and it gets fixed — the calculation is corrected, the tests are extended so the same mistake cannot come back, and the last-reviewed date on the affected pages moves.

When reporting a problem, the useful details are the two dates you entered, the figure the calculator produced and the figure you expected — that is normally enough to reproduce it in a minute. Where the disagreement is with a manual rather than with the arithmetic, quoting the instrument and edition helps most.

Every calculation runs in your browser. Dates of birth are never transmitted to a server, never logged and never stored — there is no account, no upload and nothing to delete afterwards. That is a deliberate design constraint rather than a feature: the dates entered here usually belong to a child on someone's caseload, not to the person typing them. Full detail is on the privacy page.

43 instrument pages, each pre-set to the age format that assessment records, with its published age range and corrected-age rule — indexed on the assessment reference. Plus these calculators:

• Chronological Age Calculator — Calculate your exact age in years, months, weeks, and days.
• Chronological Age in Months Calculator — Calculate chronological age in months for testing and assessments.
• Assessment Age Calculator — Enter dates once and get every age format used in school assessment workflows.
• Biological Age Calculator — Explore an educational lifestyle age score and its clinical limitations.
• Pearson Age Calculator — Calculate age in the format required for Pearson assessments.
• Brigance Chronological Age Calculator — Calculate chronological age in years;months for Brigance developmental assessments.
• Adjusted Age Calculator — Calculate adjusted (corrected) age for premature babies.
• Dog Years Calculator — Convert your dog's age to human years using modern formulas.
• Cat Years Calculator — Convert your cat's age to human years.
• Korean Age Calculator — Convert your age to the Korean age system.
• Age Difference Calculator — Calculate the exact age difference between two people.
• Birthday Calculator — Find out how many days until your next birthday.
• Retirement Age Calculator — Calculate when you can retire and plan for the future.

These calculators are informational and educational tools. The biological age calculator is an estimate from general lifestyle factors and is not a medical assessment. Corrected-age output is not medical advice — follow your paediatrician or clinical team.

For educational assessment, treat the output as a cross-check rather than a source of authority: verify the format and the age range against the manual for the edition you are administering, and follow your district, state or agency rules where they are more specific than the publisher's.