NHS Age Calculator
This independent UK age calculator works out chronological age from a date of birth to a chosen reference date. It can be useful when an NHS or clinical assessment needs age on a particular date rather than a rough age based only on birth year.
Calculate chronological age
Chronological age:
What is chronological age?
Chronological age is the time elapsed since birth. RCPCH describes chronological age as time elapsed since birth and distinguishes it from corrected age used in some assessments of children born preterm.
How the calculator works
The tool compares the date of birth with the selected reference date and returns completed calendar years, months and remaining days. It uses calendar dates rather than assuming every year has 365 days or every month has the same length.
Why a reference date matters
Age may be needed at the date of an appointment, assessment, admission or other event. NHS data standards use a person’s birth date in age-related data items, so using the correct date of birth and relevant event date matters when exact age is required.
Worked example
A person born on 10 March 2000 is 26 years, 6 months and 7 days old on 17 September 2026.
Chronological age versus corrected age
This tool returns chronological age only. RCPCH defines corrected age for preterm infants separately as chronological age minus the number of weeks preterm. Do not use this calculator as a substitute for a clinician’s corrected-age or developmental assessment.
Limitations
This calculator does not determine eligibility for NHS treatment, benefits, screening, vaccination or any other age-dependent service. Those services can have their own rules and cut-off dates. It also does not calculate biological age or heart age.
Authoritative Sources
- NHS Data Model and Dictionary: Person Birth Date
- RCPCH UK-WHO Growth Charts: chronological and corrected age
Related Calculators
NHS 18 Week Calculator · NHS Calculator · NHS DNA Rate Calculator · NHS Pregnancy Calculator · Ovulation Calculator NHS
FAQs
What does the NHS age calculator calculate?
It calculates chronological age in completed years, months and days between a birth date and a selected reference date.
Can I calculate age on a past date?
Yes. Enter the past appointment, assessment or other relevant date as the reference date.
Is chronological age the same as corrected age?
No. Corrected age may be used for some preterm infants and is calculated differently.
Does this calculator decide NHS eligibility?
No. Individual NHS services can have separate age and eligibility rules.
Disclaimer: General date-calculation information only. This is not an official NHS service and does not determine clinical or service eligibility.