What this calculator does
Gestational age from crown-rump length works out dates an early pregnancy from a first-trimester ultrasound measurement. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaGA (days) = 8.052 × √(CRL × 1.037) + 23.73, CRL in mm (Robinson & Fleming, corrected equation)
The inputs explained
| Field | What to enter |
|---|---|
| Crown-rump length (mm) | A number, measured in mm. Starts at 20. |
| Scan date | A calendar date. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with crown-rump length
Every other input is held at the calculator’s starting values while crown-rump length varies. Select any row to load that scenario into the calculator.
How the answer changes with crown-rump length
| Crown-rump length (mm) | Estimated gestational age | Gestational age (days) | Estimated due date |
|---|---|---|---|
| 10 | 7 weeks 1 days | 49.7 days | 27 Mar 2027 |
| 15 | 7 weeks 6 days | 55.5 days | 21 Mar 2027 |
| 20 | 8 weeks 4 days | 60.4 days | 16 Mar 2027 |
| 30 | 9 weeks 6 days | 68.6 days | 8 Mar 2027 |
| 40 | 10 weeks 6 days | 75.6 days | 1 Mar 2027 |
| 60 | 12 weeks 3 days | 87.2 days | 17 Feb 2027 |