Due date formula
Due date = Conception date + 266 days
Pregnancy trimesters
| Trimester | Weeks | Milestones |
|---|---|---|
| First | Weeks 1–13 | Organs form; first prenatal visit and dating ultrasound |
| Second | Weeks 14–27 | Anatomy scan around 18–22 weeks; movement felt |
| Third | Weeks 28–40+ | Rapid growth; full term from 39 weeks |
A pregnancy is considered full term from 39 weeks 0 days to 40 weeks 6 days, early term from 37 weeks, and preterm before 37 weeks.
This tool gives an estimate only. Your healthcare provider will confirm your due date, usually with an ultrasound.
How to use the calculator
- Choose the method: first day of your last menstrual period (LMP), conception date, or IVF transfer date.
- Enter the date and, for the LMP method, your usual cycle length.
- Read your estimated due date, how many weeks pregnant you are today, your trimester and key dates.
How accurate is a due date?
Only about 4–5% of babies arrive on their exact due date. Most are born within two weeks either side. Since 2013 the American College of Obstetricians and Gynecologists (ACOG) classifies births as early term (37 weeks 0 days to 38 weeks 6 days), full term (39 weeks 0 days to 40 weeks 6 days), late term (41 weeks) and post-term (42 weeks or more). An ultrasound in the first trimester measuring the baby’s crown-rump length is the most accurate way to date a pregnancy, and your provider may adjust the due date based on it.
IVF due dates
With IVF, the conception date is known precisely. For a day-5 blastocyst transfer, the due date is the transfer date + 261 days; for a day-3 embryo transfer, + 263 days.
Key milestones
- Weeks 4–6: a home pregnancy test is usually positive; first prenatal visit typically scheduled around week 8.
- Weeks 10–13: first-trimester screening and cell-free DNA testing options.
- Weeks 18–22: the detailed anatomy ultrasound.
- Weeks 24–28: glucose screening for gestational diabetes.
- Weeks 35–37: group B strep test.
Healthy pregnancy basics
- Take a daily prenatal vitamin with at least 400 micrograms of folic acid, ideally starting before conception.
- Avoid alcohol, smoking and recreational drugs; limit caffeine to under 200 mg a day.
- Avoid high-mercury fish, unpasteurized dairy and undercooked meat and eggs.
- Stay active unless your provider advises otherwise — about 150 minutes of moderate activity a week is recommended.
This calculator provides an estimate for information only. Always follow the advice of your doctor or midwife, and contact them promptly about bleeding, severe pain, fluid leakage or reduced baby movements.