Woods Method Due Date Calculator
Free Woods Method Due Date Calculator: enter your last period date or conception date to calculate your due date, current week, and key pregnancy milestones.
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What Is the Woods Method Due Date Calculator?
A pregnancy calculator estimates your due date, current gestational age, and key trimester milestones based on your last menstrual period (LMP) or conception date. Gestational age is measured from the LMP, not conception — which means a full-term pregnancy is 40 weeks from LMP even though actual conception typically occurs around week two.
Who Should Use This Calculator?
This tool is designed for:
- Newly pregnant individuals confirming their due date before the first ultrasound
- Partners and family members tracking key pregnancy milestones
- People who have irregular cycles and want to estimate conception more precisely
- Anyone who has experienced a loss and wants to understand risks by gestational age
- Healthcare students learning standard obstetric date calculations
Key Concepts Explained
- Naegele's Rule
- The standard due date formula: add 9 months and 7 days (or 280 days) to the first day of your last menstrual period. It assumes a 28-day cycle with ovulation on day 14.
- Gestational vs. Fetal Age
- Gestational age is measured from the LMP; fetal age is measured from conception. Gestational age is 2 weeks longer than fetal age. Doctors always use gestational age.
- Trimester Breakdown
- First trimester: weeks 1–13. Second trimester: weeks 14–27. Third trimester: weeks 28–40+. Key developmental milestones, prenatal tests, and screening windows are tied to these periods.
- Ultrasound Dating
- If LMP-based dating and ultrasound dating differ by more than 7 days (in the first trimester) or 14 days (later), the ultrasound date is generally used to set the official due date.
- Full Term Definition
- As of 2013, ACOG defines term pregnancy as 39 0/7 to 40 6/7 weeks. Early term is 37–38 weeks; full term is 39–40 weeks; late term is 41 weeks; post-term is 42+ weeks.
Tips for Best Results
- Schedule your first prenatal appointment (8–10 weeks) as soon as your pregnancy is confirmed
- Start prenatal vitamins with at least 400 mcg of folic acid immediately — neural tube formation occurs in the first 28 days
- Know your key screening windows: NIPT (10–13 weeks), nuchal translucency (11–13 weeks), anatomy scan (18–20 weeks), glucose test (24–28 weeks)
- Avoid alcohol, smoking, and raw/undercooked foods throughout pregnancy
- Ask your provider about Group B Strep testing, typically done at 35–37 weeks
Frequently Asked Questions
How accurate is a due date?
Only about 5% of babies are born on their exact due date. Most births occur within two weeks before or after. The due date is best understood as the midpoint of a window, not a precise prediction.
What should I do as soon as I find out I am pregnant?
Call your OB, midwife, or family doctor to schedule a first prenatal visit. Start prenatal vitamins if you haven't. Avoid alcohol, raw seafood, high-mercury fish, unpasteurized cheeses, and deli meats. Stay well hydrated.
What is the risk of miscarriage?
Approximately 10%–20% of known pregnancies end in miscarriage, with the vast majority occurring in the first trimester. Risk drops significantly after a heartbeat is detected at 6–8 weeks.
Can I travel during pregnancy?
Generally yes, through about 36 weeks for domestic travel. International travel is typically fine in the second trimester. Air travel is generally safe, but check your airline's policy and consult your provider about blood clot prevention on long flights.