Pregnancy Due-Date Calculator
Estimate your due date from your last period.
Reviewed by Zerunio’s medical team
Your estimated due date is worked out from the first day of your last period, assuming a 40-week pregnancy. A dating scan in early pregnancy gives a more precise date.
This tool gives general estimates for education only – it is not medical advice. Talk to a clinician about your health.
Frequently asked questions
How is my due date calculated?
By adding 280 days (40 weeks) to the first day of your last period, then adjusting for your cycle length. It assumes ovulation around day 14.
How accurate is the due date?
Only about 1 in 20 babies arrive on the exact date. Most are born within two weeks either side. An early ultrasound gives the most accurate estimate.
What if my cycle is irregular?
The period-based estimate is less reliable with irregular cycles. A dating scan is the best way to confirm how far along you are.
When should I see a doctor?
Book antenatal care as soon as you know you're pregnant so you can get a scan, screening, and advice for a healthy pregnancy.