Chronological Age Calculator
Chronological age means the age on a particular day, usually the day an assessment was given rather than the day the form is being filled in. This page opens with that second date field showing: enter the date of birth, enter the date you are measuring at, and the answer comes back in years, months and days. Leave the As of field empty and it is the age today.
Set the date you want the age measured on: a test date, an assessment date, a deadline. While it is empty the answer is the age today.
Chronological age on 1 September 2026, by date of birth
Computed with the tool's own calculation for a fixed assessment date of Tuesday 1 September 2026, for children born on the first of each month over one year. It shows the shape of the answer rather than being a lookup table: put your own two dates into the tool above for the exact figure. Whole calendar months are counted first and the days left over after that, which is why one month of difference is not always the same number of days.
| Date of birth | Age on 1 September 2026 | In months | In days |
|---|---|---|---|
| September 1, 2020 | 6 years | 72 months | 2,191 days |
| October 1, 2020 | 5 years, 11 months | 71 months | 2,161 days |
| November 1, 2020 | 5 years, 10 months | 70 months | 2,130 days |
| December 1, 2020 | 5 years, 9 months | 69 months | 2,100 days |
| January 1, 2021 | 5 years, 8 months | 68 months | 2,069 days |
| February 1, 2021 | 5 years, 7 months | 67 months | 2,038 days |
| March 1, 2021 | 5 years, 6 months | 66 months | 2,010 days |
| April 1, 2021 | 5 years, 5 months | 65 months | 1,979 days |
| May 1, 2021 | 5 years, 4 months | 64 months | 1,949 days |
| June 1, 2021 | 5 years, 3 months | 63 months | 1,918 days |
| July 1, 2021 | 5 years, 2 months | 62 months | 1,888 days |
| August 1, 2021 | 5 years, 1 month | 61 months | 1,857 days |
Common questions
- What is chronological age?
- The time actually elapsed since birth, measured to a stated date. Educators, psychologists and clinicians use the phrase because the figure a test norm needs is the age on the day of the test, which is often weeks or months before the report is written. It is not an estimate and it is not adjusted for anything: it is calendar arithmetic between two dates.
- How do I get the age on a date other than today?
- Age at is already set to A set date on this page, so the As of field is on screen. Put the test or assessment date in it. Every figure under the result then describes that day, and the line above the table says so. Switch Age at back to Today and the As of field goes away, and the answer is the age right now again.
- Why years, months and days rather than a decimal?
- Because a year is not a fixed number of days and a month is not a fixed number of days either, so dividing by 365.25 gets birthdays wrong by a day around leap years. This tool counts whole calendar months from the date of birth and then the days left over, which is the same convention test manuals use when they ask for an age in years and months.
- What happens with a 29 February birthday?
- In a common year there is no 29 February, and the two conventions in use disagree by a day. This tool uses the more common one: the anniversary falls on 1 March, so somebody born on 29 February 2004 turns 21 on 1 March 2025, not on 28 February. The tool says so on the page rather than making the choice silently.
- What if the date of birth is after the date I am measuring at?
- The tool says the two dates are the wrong way round and asks you to check which field holds which, rather than showing a negative age. Nothing is guessed or swapped for you.
- Is anything sent anywhere?
- No. The dates never leave your browser, there is no account, and the calculation runs in the page. A date of birth typed into the first field is kept in your own browser so it is there next time; the As of date is not kept, because it belongs to one assessment rather than to you.
Exact, and it states the leap-day convention it used rather than picking one silently.