How is due date calculated?

Using Naegele's Rule: add 280 days (40 weeks) to the first day of the last menstrual period (LMP). For conception date, add 266 days. For IVF, based on embryo transfer date and embryo age.

Can I use imperial units?

This calculator uses standard calendar dates. Cycle length is in days—universal.

Professional Pregnancy Calculator — Due Date, Week & Milestones

Q: How accurate is the due date?

Only about 5% of babies arrive on the exact due date, but 80% are born within two weeks (before or after). First‑trimester ultrasound improves accuracy.

Q: What is the difference between gestational age and fetal age?

Gestational age counts from LMP (about 2 weeks before conception). Fetal age counts from actual conception. Medical providers use gestational age.

Understanding Your Pregnancy Timeline

Pregnancy is measured in weeks from the first day of the last menstrual period (LMP). A full‑term pregnancy lasts about 40 weeks, divided into three trimesters. This Professional Pregnancy Calculator uses your input to estimate due date, current gestational age, trimester, and important prenatal milestones. It supports LMP, conception date, and IVF transfer methods.

Calculation Methods

LMP Method: Adds 280 days to LMP, adjusted for cycle length (longer cycles delay due date).
Conception Method: Adds 266 days (38 weeks) from estimated conception date.
IVF Method: Uses embryo transfer date and embryo age (Day 3 or Day 5) to back‑calculate LMP, then applies standard 280‑day gestation.

💡 When Is Full Term?

Full term is 39 weeks 0 days through 40 weeks 6 days. Early term is 37‑38 weeks. Babies born at full term have the best health outcomes.

Key Milestones

Week 4: Implantation complete. Week 6: Heartbeat detectable. Week 12: End of first trimester. Week 20: Anatomy scan. Week 24: Viability milestone. Week 28: Third trimester begins. Week 37: Early term.

Frequently Asked Questions

How accurate is the due date?

Only ~5% deliver on the exact date. Most (80%) deliver between 38‑42 weeks. First‑trimester ultrasound is the most accurate dating method.

What if my cycle is irregular?

Use the conception date method if known, or enter your average cycle length. An early ultrasound is recommended for accurate dating.

How is IVF due date different?

IVF dating is more precise because the date of fertilization/transfer is known. The calculator adjusts based on embryo age (Day 3 or Day 5).

What is the difference between gestational age and fetal age?

Gestational age is counted from LMP (~2 weeks before conception). Fetal age counts from actual conception. Medical providers use gestational age.

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