Age calculator — years, months & days
Get the precise age in years; months; days between a date of birth and any date — the way clinical assessments and IEP paperwork want it. Enter two dates and read the exact Y;M;D, leap-aware and correct at every month boundary.
Corrected age for prematurity
Corrected age subtracts the weeks born early from the term due date. Many clinicians stop correcting at 24 months (AAP) — some protocols use 36. Follow your own protocol; this is a labelled default, not a rule.
How we calculate this
Score a whole caseload at once. Rows are saved in this browser only — no accounts, nothing uploaded.
| Student | Date of birth | Test date | Age |
|---|
- Exact Y;M;D between any two dates, leap-aware.
- Caseload mode — do a whole roster in one pass.
- Private — dates never leave your browser.
Age in years, months and days, done exactly
Most everyday calculators give you an age as a single number of years, or a total number of days. Clinical and educational work needs something more precise: the age broken into whole years, whole months and leftover days. This page returns exactly that between any date of birth and any end date, and it is built to match the careful calendar arithmetic an examiner would do by hand.
What years; months; days means
Years; months; days (often written Y;M;D) counts the completed years first, then the completed months since the last birthday, then the days left over. A child born 18 May 2011 and measured on 6 February 2024 is 12;8;19 — twelve years, eight months and nineteen days. The value is never ambiguous: months never reach 12 (they roll up into a year) and days never reach a full month (they roll up into a month).
How the calendar borrowing works
The calculation subtracts day, then month, then year, borrowing when it needs to. If the end day falls before the birth day, it borrows the length of the preceding month so the day count stays positive; if the month then falls short, it borrows a year. Because the borrow uses the real length of each month, the result is leap-aware and clamps month-end dates correctly, so it always agrees with a careful date-difference rather than a rough 30-day-month estimate.
Where the Y;M;D format is used
Norm-referenced tests select an age band from the exact years; months; days at testing. IEP eligibility and re-evaluation paperwork records age in the same form. Pediatric and developmental milestone checks — motor, speech, feeding — are charted against age in months, which the Y;M;D value gives you directly. In every case the precise figure, not a rounded year, is what keeps the comparison valid.
A note on rounding
This tool defaults to the exact age and also offers years; months only (dropping the days) and rounding the month at the 15-day mark. Which convention is correct depends entirely on the specific assessment's manual — we never assume a rule a manual doesn't state, so pick the mode that matches the test you are scoring.
Related ChronoAge Pro tools
Years, months & days — FAQ
What is age in years and months?
Age in years and months expresses how old someone is as a whole number of years plus the extra completed months — for example, 6;5 means six years and five months old. Clinicians write it as years; months; days (Y;M;D) so a single value carries the precision a norm-referenced test needs. This tool shows the full years; months; days and can drop the days to years and months when you need that shorter form.
How do I calculate age in dd/mm/yyyy?
Enter the date of birth and the end date using the date picker; the display format (dd/mm/yyyy or mm/dd/yyyy) follows your device settings and does not change the result. The calculator subtracts the two calendar dates and returns the elapsed time as years; months; days, borrowing across months and years exactly the way a careful hand calculation does.
How do you calculate age with years and months?
Start from the day, then the month, then the year. If the end day is earlier than the birth day, borrow a month (the days of the previous month) so the day count stays positive; if the end month is then earlier than the birth month, borrow a year. What remains is the age in whole years, whole months and leftover days — the years; months; days value shown here.
What is 12 months in age?
Twelve completed months equal exactly one year, so an age of 12 months is written 1;0;0 — one year, zero months, zero days. The calculator rolls a full 12 months up into a year automatically, so you never see a months field of 12; it becomes an extra year instead.
Does it handle leap years and month-ends?
Yes. The counting is leap-aware, so a February 29 birthday and any span crossing a leap day are handled correctly, and month-end dates are clamped to the real last day of the shorter month. The result always matches a careful calendar date-difference; open “How we calculate this” to see the working for your own dates.