Pregnancy due date calculator
Pregnancy is usually dated from the first day of your last menstrual period (LMP). An estimated due date is 280 days (40 weeks) after that date, assuming a 28-day cycle. Only about 1 in 20 babies arrive on their due date; most are born within a couple of weeks either side.
The three trimesters
| Trimester | Weeks |
|---|---|
| First | Week 1 to the end of week 13 |
| Second | Week 14 to the end of week 27 |
| Third | Week 28 to birth |
Good to know
- This is an estimate. An early ultrasound scan usually gives a more accurate due date, and your doctor or midwife may change your date after it.
- If your cycles are irregular, or you're not sure of the date of your last period, the estimate may be less accurate.
- If you think you're pregnant, see a doctor, midwife or clinic early to start prenatal (antenatal) care.
- Get urgent medical help for heavy bleeding, severe belly pain, a severe headache with vision changes, fluid leaking from the vagina, or if your baby is moving less than usual later in pregnancy.
Sources
- American College of Obstetricians and Gynecologists (ACOG): Methods for estimating the due date
- MedlinePlus: Prenatal care
- Office on Women's Health (HHS): Stages of pregnancy