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Pearson Age Calculator: Age in Y;M;D Test Format

What is this tool?

The Pearson age calculator gives a person's chronological age on a test date, written in the format assessment reports use: years;months;days, for example 36;5;8. It is the format used in Pearson-style assessment reports, where a single compact figure has to carry the exact age, because test scores are interpreted against age norms for the day of testing, not against age today. Enter the date of birth and the test date below and you get the age in that format, plus the same age written out in full and in total months, so it can be copied straight into a report.

How it works

It uses the borrowing method taught in assessment training: subtract the birth year, month and day from the test year, month and day, borrowing a month when the test day is smaller than the birth day, and borrowing a year when the test month is smaller. That is the same exact calendar arithmetic as the main age calculator, but with the test date as the reference date instead of today, and with the result written as Y;M;D. The result is the person's chronological age, which is calendar age from birth. It is not a corrected age, which adjusts for prematurity and is a different calculation on its own page.

Worked example

Worked example: born 15 May 1990, tested on 23 October 2026. Borrowing gives 36 years, 5 months and 8 days, written 36;5;8, which is 437 total months plus 8 days. That is the figure a Pearson-style report would carry for this person on that test date.

When to use it

The people who need this format are the people who write or read assessment reports. A psychologist, speech-language therapist, educational assessor or teacher scoring a test needs the age on the test date, because the norms tables are organised by age at testing, and a child tested in October and scored in December must be scored at the October age, not the December age. Parents sometimes need it too, when a report arrives with a figure like 10;4;13 and nobody has explained what the semicolons mean.

The test date is the whole point of this page. The main age calculator answers age today, which is the wrong date whenever the test happened days, weeks or months ago. A report written in January about a test taken in November must carry the November age, and using today's age instead overstates the child's age and can push the score into the wrong norm band. This page exists so that the test date, not today, is the reference date.

• Psychologists and assessors writing chronological age into a test report in Y;M;D format.
• Speech-language therapists and occupational therapists scoring against age norms.
• Teachers and SENCOs checking the age figure quoted in an assessment report.
• Parents reading a report and wanting to check the age figure themselves.
• Researchers recording age at testing consistently across participants.
• Anyone converting an age in years and months into the compact semicolon format.

This calculator is an independent tool that follows the same Y;M;D format used in assessment reports. It is not affiliated with, endorsed by, or published by Pearson, and it does not score any test. It calculates age only; interpreting a test score against norms is the assessor's job.

Step by step

Using this page takes two dates and gives one compact figure, plus the same figure written out in full so it can be checked.

1. Enter the date of birth in the first field. This is the birth date on the report, not today's date.
2. Enter the test date in the second field. This is the date the test was actually taken, even if the report is being written later.
3. Read the headline result first: the age written as years;months;days, for example 36;5;8. That is the figure to copy into a report.
4. Read the full wording underneath: the same age in years, months and days, plus total months. Use it to check the compact figure before copying it.

The borrowing method behind the result is worth understanding, because it explains why the days figure is never larger than the days in a month. When the test day is smaller than the birth day, a month is borrowed, so the days figure counts from the borrowed month's length, not from a fixed 30 days. That is why the same pair of dates always gives the same result here as it would from a careful hand calculation, and why dividing total days by 30 would give a different, wrong answer.

One practical note: keep the test date with the result when you copy it. A figure like 36;5;8 is only meaningful with its test date attached, because the same person has a different figure on every other date. Reports that quote the age without the test date force the reader to guess which date it belongs to, and that guess is where errors start.

Common mistakes

The most common mistake is using today instead of the test date. It is the easiest mistake to make, because the main age calculator defaults to today, and the difference looks small when the test was recent. But norms bands are narrow, and even a few weeks can matter for a young child, so the test date must be entered even when it feels like a formality. If the test date is not known, find it before calculating, rather than substituting today.

The second mistake is reading the semicolon format as a decimal. 36;5;8 does not mean 36.58 years, and it does not mean 36 and a half years. It means 36 completed years, 5 completed months and 8 days, which is 437 months and 8 days. Converting it to a decimal for a spreadsheet loses the exactness the format exists to preserve, so keep it in semicolon form in reports and convert only when a system genuinely requires a decimal.

• Using today's date instead of the actual test date, overstating the age.
• Reading 36;5;8 as a decimal number instead of years, months and days.
• Dividing total days by 30 to get months, which drifts from calendar months.
• Forgetting February 29 birthdays, which count as 28 February in non-leap years here.
• Using this page for a premature child without checking whether a corrected age is required instead.
• Copying the age figure into a report without its test date.

A further mistake is confusing chronological age with corrected age. Chronological age counts from the actual birth date, always. Corrected age counts from the due date and is used for young children born early. If a report is about a premature child under two, ask whether the report should carry chronological age, corrected age, or both, before choosing a page. This page gives chronological age only.

More worked examples and notes

The examples below are all calculated with the same borrowing method, and each can be checked by entering the same two dates into the tool.

• Born 15 May 1990, tested 14 April 2026: 35;10;30, which is 430 total months plus 30 days. This is the same pair of dates used in the worked example on the chronological age page, and the two pages agree, as they should.
• Born 10 June 2015, tested 23 October 2026: 11;4;13, which is 136 total months plus 13 days. A report for this child would carry 11;4;13 as the chronological age at testing.
• Born 31 January 2016, tested 28 February 2026: 10;0;28. The months figure is zero because the test day, 28 February, is before the birth day of the month, so a month is borrowed and the days figure counts from January's 31 days: 28 plus 31 minus 31 equals 28.
• Born 29 February 2000, tested 28 February 2025: 25;0;0. February 29 birthdays are counted as turning a year older on 28 February in non-leap years, the same convention as the main age calculator.
• Born 15 May 1990, tested 15 May 2026: 36;0;0, a whole number of years, which is the cleanest possible case and a useful check that the tool is working.

A note on the format itself: the semicolon form is compact, but it is not the only form in use. Some reports write the same age as 36 years 5 months, some as 36-5, and some give total months only. When a report's style guide asks for a different form, the full wording and total months under the headline result give everything needed to rewrite the figure without recalculating it.

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Frequently asked questions

Written and checked against the calculator above. Last updated: 23 October 2026. Calculation runs entirely in your browser — no date is sent to a server. This tool gives calendar results only, not medical, legal or financial advice.