Pregnancy Due Date Calculator
Estimated due date and current stage from your last period.
Health information notice
This tool gives a general estimate only. It is not a diagnosis, a medical device or a substitute for professional advice. Simple formulas cannot account for your individual circumstances — the assumptions and limitations listed below describe the groups this model is not suitable for.
If the result concerns you, or you are making any health decision based on it, speak to a GP, midwife, pharmacist or other qualified health professional. The health figures you enter are used only to calculate your result and are not intentionally retained — see our privacy policy.
About this calculator
The estimated due date is calculated with Naegele's rule: 280 days from the first day of your last menstrual period, adjusted for your cycle length (a 35-day cycle typically means later ovulation, so the due date shifts later too). This calculator gives the date, your current week and trimester, and the countdown.
The formula
Worked example
LMP 10 June 2026, 28-day cycle: due 17 March 2027. On 18 July you'd be 5 weeks 3 days — first trimester.
Common mistakes
- Counting from conception instead of the LMP — pregnancy weeks start at the LMP by convention.
- Ignoring cycle length: a 35-day cycle shifts the estimate a week later.
- Planning around the exact date — only ~5% of babies arrive on it.
Frequently asked questions
Assumptions & limitations
Naegele's rule with cycle adjustment. Informational only — your midwife's dating takes precedence.
Sources & verification
- NHS — pregnancy due date calculator — NHS guidance on estimating a due date from the last menstrual period
- NICE guideline NG201 — antenatal care — Clinical guidance; a dating ultrasound scan gives a more accurate due date than any calculation
All sources last accessed 24 July 2026.
Spotted an error or an out-of-date figure? Report it — corrections are prioritised over all other work (see our corrections policy).