How the due date calculator works
Your estimated due date (EDD) is the day you reach 40 weeks of pregnancy. This calculator uses Naegele's rule — 280 days from the first day of your last menstrual period — and adjusts for your cycle length. If you know your conception date instead, it counts 266 days forward.
The three trimesters
- First trimester — weeks 1 to 12
- Second trimester — weeks 13 to 26
- Third trimester — weeks 27 to 40 (and up to 42)
Getting prenatal care in Canada
Prenatal care is covered by provincial health insurance. If you have a family doctor, book with them; if not, a walk-in clinic near you can confirm the pregnancy and refer you to a doctor or midwife. Learn more about family practices on CanClinics.
Frequently asked questions
How is my due date calculated?
The standard method (Naegele's rule) counts 280 days — 40 weeks — from the first day of your last menstrual period, assuming a 28-day cycle. If your cycle is longer or shorter, the estimate shifts accordingly. From a known conception date, it's about 266 days.
How accurate is a due date?
It's an estimate. Only about 4–5% of babies are born on their exact due date; most arrive within the two weeks either side. An early ultrasound (usually 8–13 weeks) gives the most accurate dating.
When should I see a doctor about a pregnancy?
Book with a family doctor, midwife, or walk-in clinic as soon as you think you're pregnant — early prenatal care matters. If you don't have a provider, a walk-in clinic can start the process and refer you.