Pregnancy stages by week
How pregnancy is divided according to the American College of Obstetricians and Gynecologists (ACOG).
| Stage | From | To |
|---|---|---|
| First trimester | Start of pregnancy | 13 weeks 6 days |
| Second trimester | 14 weeks | 27 weeks 6 days |
| Third trimester | 28 weeks | Birth |
| Early term | 37 weeks | 38 weeks 6 days |
| Full term | 39 weeks | 40 weeks 6 days |
| Late term | 41 weeks | 41 weeks 6 days |
FAQ
How does the calculator work out how far along I am?
Pregnancy is counted from the first day of your last period, not from conception, so you’re already about “3 weeks pregnant” when conception happens. A full pregnancy is 280 days (40 weeks) from that day.
Why is gestational age different from the baby’s age?
The baby’s age starts at conception, about two weeks after your last period in a regular cycle, so it’s about two weeks less. Doctors and scans use gestational age.
My cycle isn’t 28 days. Does that change anything?
Yes. Enter your cycle length: with a 32-day cycle, for example, we shift the dates by 4 days because ovulation comes later. If your cycle is irregular, an ultrasound is more accurate.
Which is more accurate, my last period or an ultrasound?
A first-trimester ultrasound is the most accurate way to date a pregnancy. If your doctor dated it by ultrasound, choose “Ultrasound” and enter it as written in the report.
How are months counted?
Months aren’t a medical unit, so we use the common split: month 1 to week 4, month 2 to week 8, month 3 to week 13, then 17, 22, 27, 31, 35 and 40.
Do you store the date I enter?
No. Everything is calculated in your browser; no date is sent anywhere.