Due Date & Pregnancy Week Calculator

Estimates the due date from the first day of the last period, the conception date or an IVF transfer date, and shows how many weeks and days pregnant you are on a chosen date. You can also enter a due date from a scan.

How to use

1. Under "Calculate from", choose "First day of last period", "Conception date", "IVF embryo transfer date" or "Due date from a scan or clinician".
2. Enter the date. Set "Usual cycle length" (20 to 45 days) if your cycle is not 28 days; for IVF, choose "Day-3 embryo" or "Day-5 embryo (blastocyst)".
3. Read the "Estimated due date", "Weeks pregnant" and the days left. Change "As of" to check another day.
4. The "Trimesters" and "Week dates" tables list the dates of milestones such as 12, 20 and 37 weeks.

How it works

• Due date = first day of the last period + 280 days, moved by the difference when the cycle is not 28 days. Conception date + 266 days; transfer date + 266 days minus the embryo age (3 or 5 days).
• Weeks count from the due date minus 280 days (week 0, day 0). Trimesters: to 13 weeks 6 days, 14 weeks to 27 weeks 6 days, 28 weeks to the due date.
• The due date is an estimate based on an average pregnancy. Confirm the weeks and the due date with your clinician (ultrasound). This calculator does not give medical advice.

Questions and answers

When do pregnancy weeks start counting?

From the first day of the last period, not from conception. Conception therefore usually falls at about 2 weeks 0 days.

How do I calculate my due date from conception?

Add 266 days to the conception date. Choose "Conception date" and the page does this for you.

Which date should I use if my scan date is different?

Follow the due date your clinician gave you. Choose "Due date from a scan or clinician" and enter it; the weeks and milestones are then based on it.

At how many weeks is a pregnancy full term?

Full term begins at 37 weeks 0 days. The row "37 weeks (full term begins)" in "Week dates" shows that date.