Quick answer
School age is a child's age on the school's cutoff date. A child born 15 March 2020 is 5 years 5 months (1,996 days) old on the cutoff date of 1 September 2025.
Enter the date of birth and the school cutoff date. The calculator returns the age on that date.
Related tools: Baby Age Calculator: A baby's age in weeks, months and days. Age Difference Calculator: Time between two birth dates. Birth Date from Age Calculator: Range of possible birth dates for someone of a given age.
How to use the School Age Calculator
- Pick date of birth.
- Pick school cutoff date.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Date of birth | A calendar date | — |
| School cutoff date | A calendar date | — |
Formula and method
Formula
age = cutoff date − birth date
IEEE-754 double precision; shown to the decimals indicated.
School entry rules vary by district, so check yours.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Date of birth = 2020-03-15; School cutoff date = 2025-09-01.
| Result | Value |
|---|---|
| Age on the cutoff date | 5 years, 5 months |
| Days old | 1996 |
Example 2
Inputs: Date of birth = 2019-09-02; School cutoff date = 2025-09-01.
| Result | Value |
|---|---|
| Age on the cutoff date | 5 years, 11 months |
| Days old | 2191 |
Example 3
Inputs: Date of birth = 2018-12-31; School cutoff date = 2024-08-15.
| Result | Value |
|---|---|
| Age on the cutoff date | 5 years, 7 months |
| Days old | 2054 |
The first line is the headline result (age on the cutoff date). Below it the school Age Calculator lists days old, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Cutoffs differ
US districts often use 1 September, others 31 July, 30 September or 1 January; England uses 31 August. The rule is that a child must reach a minimum age, commonly 5, by the cutoff date.
Redshirting
Some families delay entry for children born just after the cutoff. This tool gives the age on the date only; the school or district decides on entry.
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- School cutoff date: entering "2025-01-01" shows "The cutoff date must not be before the birth date." beside that field and no result.
- Date of birth: left empty shows "Enter date of birth." beside that field and no result.
Choosing between the School Age Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Baby Age Calculator](/lifestyle/baby-age/) | date of birth and reference date | Age |
| [Age Difference Calculator](/lifestyle/age-difference-calculator/) | first birth date and second birth date | Age difference |
| [Birth Date from Age Calculator](/lifestyle/age-to-birthday/) | age in years and reference date | Possible birth dates |
| [Birthday Calculator](/lifestyle/birthday/) | date of birth and reference date | Next birthday |
| [Half Birthday Calculator](/lifestyle/half-birthday/) | date of birth | Half birthday |
Assumptions and limitations
- Cutoff cannot precede birth
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for school cutoff date and date of birth to confirm this.
Frequently asked questions
How old must a child be for kindergarten?
Commonly 5 by the cutoff date.
How do I find the cutoff?
Ask the school district.
Can I use any date?
Yes. Enter any cutoff date, such as 1 September or 31 December, to compare cutoffs.
What does the School Age Calculator calculate?
Child's age on a school cutoff date. It returns Age on the cutoff date and Days old.
What formula does the School Age Calculator use?
age = cutoff date − birth date. School entry rules vary by district, so check yours.
What do I need to enter in the school Age Calculator?
You enter Date of birth and School cutoff date.
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Cutoff cannot precede birth.
What is an example of a school Age result?
With date of birth 2020-03-15 and school cutoff date 2025-09-01, the age on the cutoff date is 5 years, 5 months.
Related calculators
- Baby Age Calculator — A baby's age in weeks, months and days.
- Age Difference Calculator — Time between two birth dates.
- Birth Date from Age Calculator — Range of possible birth dates for someone of a given age.
- Birthday Calculator — Next birthday, days until it, and your current age.
- Half Birthday Calculator — The date six months after a birthday.
- Age Calculator — Calculate your exact age in years, months and days.
Sources
- ISO 8601-1: Date and time, representations for information interchange (calendar dates, ordinal dates and week dates)
- Gregorian calendar reform, papal bull Inter gravissimas (1582): the leap-year rule used for all dates
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.