Chronological Age Cheat Sheet
Quick reference for clinical age calculation: subtract birth date from testing date using the borrowing method, report in Y;M;D format, apply publisher-specific rounding, and verify with the chronological age calculator. All calculations should use the testing date — not today.
The Borrowing Method (3 Steps)
- Days: Target day − Birth day. If negative, borrow days from previous month (use actual month length).
- Months: Target month − Birth month (minus any borrowed month). If negative, borrow 12 months from year.
- Years: Target year − Birth year (minus any borrowed year).
Y;M;D Format
- Semicolons as separators — not hyphens or slashes
- Two-digit months and days:
8;07;20 - Years not padded:
10;03;14 - Always calculate to the testing date
Cumulative Months
Months = (Years × 12) + Months
Example: 8y 3m = 99 months. Days not included unless protocol specifies rounding.
Publisher Format Summary
| Assessment | Format | Rounding | Example |
|---|---|---|---|
| CELF-5, WIAT-4, GFTA-3, PPVT-5 | Y;M;D | Exact (no rounding) | 7;02;14 |
| WISC-V, BASC-3 | Y;M | Days ≥ 16 → round up month | 10;03 |
| Brigance Early Childhood | Y;M;D | Exact (no rounding) | 4;02;11 |
| Vineland-3 | Y;M;D | Exact | 5;08;22 |
Leap Year & Month Length Notes
- February: 28 days (29 in leap years). Check the year when borrowing across February.
- Leap year rule: Divisible by 4, except century years unless divisible by 400.
- 31-day months: Jan, Mar, May, Jul, Aug, Oct, Dec.
- 30-day months: Apr, Jun, Sep, Nov.
- Month-end birthdays: Born on the 31st? Use the actual last day of the target month when borrowing.
- Feb 29 birthdays: Publisher conventions vary (Feb 28 vs Mar 1 in non-leap years) — check the manual.
Common Errors to Avoid
- Using today's date instead of the testing date
- Unpadded months/days (
8;7;5instead of8;07;05) - Applying WISC rounding to CELF-5 (different rules)
- Forgetting to reduce month/year after borrowing
- Using corrected age for school-age norm-referenced tests
Tools: chronocalc.org/chronological-age-calculator.htmlchronocalc.org/chronological-age-calculator · chronocalc.org/demo.html · chronocalc.org/cheat-sheet.html
ChronoCalc — local-only calculation. No dates uploaded. Verify against current publisher manuals.
Quick Questions
Can I print this cheat sheet for my desk or assessment kit?
Yes. Click the Print Cheat Sheet button or use Ctrl+P / Cmd+P. Print styles hide navigation and format the content for a single-page reference. You can also download the Quick Reference PDF for a pre-formatted card.
What is the fastest way to calculate age during an evaluation?
Use the chronological age calculator with the testing date as target date, then copy Y;M;D directly to your score sheet. This cheat sheet is for verification and training — not a substitute for the calculator during live testing.