About the due date calculator
Doctors estimate a due date by counting 40 weeks (280 days) from the first day of your last menstrual period, known as Naegele's rule. If your cycle is longer or shorter than 28 days, the date shifts to match when you likely ovulated, which this calculator accounts for.
Your due date is an estimate. Most babies are born between 37 and 42 weeks.
Formula
Due date = first day of last period + 280 days + (cycle length − 28 days).
Frequently asked questions
How accurate is a due date?
Only about 4% of babies are born on the due date, but most arrive within two weeks either side. An early ultrasound can improve accuracy.
How many weeks pregnant am I?
Pregnancy is counted from the first day of your last period, so you are considered 4 weeks pregnant around the time of a missed period.
These calculators give general estimates and are not medical advice. Talk to a doctor or registered dietitian before changing your diet or exercise routine.