Pregnancy Due Date Calculator
Estimate your due date from your last menstrual period.
About this tool
This calculator uses Naegele's rule — the standard clinical formula — to estimate your due date from the first day of your last menstrual period (LMP), adjusted for cycle length.
An early ultrasound between 8 and 12 weeks remains the most accurate way to confirm your dating, and your clinician may revise the due date based on that scan.
Frequently asked questions
How accurate is the LMP method?
It's correct within about a week for people with regular 28-day cycles. Irregular cycles or uncertain LMP dates make the estimate less reliable — early ultrasound is then preferred.
Should I count from conception or LMP?
Pregnancy is dated from the first day of your last period — about 2 weeks before actual conception. That's why a 'full-term' pregnancy is described as 40 weeks.
What if I'm past 40 weeks?
Many pregnancies go a few days past the due date. Beyond 41–42 weeks, your clinician will discuss monitoring or induction.
⚕️ Educational only — not a substitute for professional medical advice, diagnosis, or treatment. In an emergency call your local emergency services.