Calculator
Pregnancy week calculator
10 weeks + 3 days means ten completed weeks and three additional days, within the eleventh week. Choose the last period, the due date established in prenatal care, or a recorded gestational age and assessment date. The check date defaults to today in Europe/Warsaw.
Calculator
Enter data
Dating basis and the date for which gestational age is calculated. Fields marked with an asterisk are required.
How to use the calculator
- If a due date is established, use it instead of re-dating the pregnancy from the last period.
- From an assessment, copy completed weeks and days, not ultrasound measurements. Choose the check date.
Calculation details
Formula and calculation method
LMP: date difference. Established due date: age = 280 days + (check date − due date). Assessment: recorded weeks × 7 + days + elapsed days since assessment. Division by 7 gives completed weeks and remaining days.
Worked example
An LMP of 1 January 2026 checked on 15 March 2026 gives 73 days: 10 weeks + 3 days. This is not 10 weeks since fertilisation.
Limitations
- LMP mode assumes the 28-day-cycle convention and does not confirm pregnancy. For uncertain dates, irregular cycles or IVF, use dating established by the care team.
- No ultrasound-measurement interpretation or clinical re-dating rules. The display range is 0–42 completed weeks; this is not a medical safety threshold.
Sources
Engine version: 2.0 (2026-09-22) · Last reviewed: 22 September 2026
Frequently asked questions
Is 10+3 in the eleventh week?
Yes. Ten weeks are complete and the next is underway. The result uses completed weeks to avoid a one-week ambiguity.
Can I use the age from an ultrasound?
Yes, using the gestational age and assessment date provided by the clinician. The calculator only adds elapsed time; it does not interpret the scan.