Pregnancy Due Date Calculator
Work out your estimated due date, how many weeks pregnant you are and your trimester — from the first day of your last period, the date of conception or an IVF transfer date.
Calculate your due date
Trimesters and term
| Stage | Weeks + days |
|---|---|
| First trimester | Up to 13w 6d |
| Second trimester | 14w 0d to 27w 6d |
| Third trimester | From 28w 0d |
| Early term | 37w 0d to 38w 6d |
| Full term | 39w 0d to 40w 6d |
| Late term | 41w 0d to 41w 6d |
| Post-term | 42w 0d and beyond |
How it is calculated
due date = first day of last period + 280 days + (cycle length − 28)
due date = conception date + 266 days
due date = transfer date + 261 days
due date = transfer date + 263 days
Dates are counted day by day rather than with the “add a year, take away three months, add seven days” shortcut, which can be up to three days out because months differ in length.
The cycle adjustment assumes ovulation about 14 days before your next period, so a 35-day cycle moves the due date 7 days later and a 25-day cycle 3 days earlier.
Guidance from the American College of Obstetricians and Gynecologists is that a first-trimester ultrasound is the most accurate way to date a pregnancy.
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For general information only — not medical advice, diagnosis or treatment. These calculators use population formulas that cannot account for every individual, and are meant for adults unless stated. Always speak to a qualified doctor about your health, and never delay seeking care because of a result here.