Yes — you can get ChatGPT, Claude, or Gemini to calculate a child's exact chronological age in years;months;days for a standardized assessment. Below is the prompt that works most reliably. But be straight about what it can't do: even this prompt still gets some real cases wrong — see where it fails.
Replace the two dates, paste it into your AI of choice, and read its working.
You are a precise date calculator. Calculate a child's chronological age for a standardized assessment. Birth date: [YYYY-MM-DD] Test date: [YYYY-MM-DD] Use the "borrow 30" convention that test publishers (e.g. Pearson Q-global) expect: 1. Subtract day-from-day, month-from-month, year-from-year. 2. If days are negative, borrow 1 month and add 30 days. 3. If months are negative, borrow 1 year and add 12 months. 4. Do NOT round. Do NOT skip a borrow. Show your subtraction step by step, then give the final answer in the exact format Years;Months;Days (e.g. 5;3;14).
Standardized tests don't use ordinary calendar age — they use the borrow-30 convention (every month counts as 30 days when you borrow a day), and that's the value Q-global and the manuals expect. A general calculator, or an AI doing calendar math, returns a different day count. Every date below is real and every value is computed:
| Birth | Test | Borrow-30 (manuals) | Plain calendar (AI / general) |
|---|---|---|---|
| Aug 31, 2014 | Sep 1, 2026 | 12;0;0 | 12;0;1 |
| Dec 31, 2014 | Jan 1, 2026 | 11;0;0 | 11;0;1 |
| May 31, 2018 | Jun 15, 2026 | 8;0;14 | 8;0;15 |
| Feb 10, 2020 | Mar 5, 2026 | 6;0;25 | 6;0;23 |
| Feb 29, 2024 | Feb 28, 2025 | 0;11;29 | 0;11;30 |
The gaps look tiny — a day or two — but the borrow-30 value is the one the manual expects and the calendar value isn't. Some dates break calendar math outright, and an AI is non-deterministic — ask twice, sometimes get two answers. For a number that sets a child's age band, you want the single deterministic value the manual expects.
→ The full breakdown: why AI and generic calculators get assessment age wrong
Yes, but not reliably out of the box. With a carefully worded prompt that specifies the borrow-30 method and forces it to show its work, it's right most of the time — but it still errors on edge cases like leap-day birthdays and month-end dates, so its output should always be verified.
It's the convention standardized test publishers use: when the day count goes negative you borrow one month and add 30 days; when the month count goes negative you borrow one year and add 12 months. It deliberately does not use the real length of each calendar month, which is why a "calendar-accurate" AI answer can disagree with what a test manual expects.
Norm-referenced assessments score children in age bands that are often only three to six months wide. Landing in the wrong band changes the standard score and percentile, and can change whether a child qualifies for services.
A deterministic calculator built for the borrow-30 method — like the free Speechies Chronological Age Calculator — gives the same correct answer every time and removes the need to verify an AI's output.