Find your estimated due date, current trimester, and key milestones in seconds.
Typical range: 20–45 days
| Milestone | Date | Week | Status |
|---|
| Week | Starts | Trimester | Days Left |
|---|
Choose your calculation method from the three tabs: Last Menstrual Period (LMP) — the most common method, enter the first day of your last period and your average cycle length; Conception Date — if you know when you conceived; or IVF Transfer — enter your embryo transfer date and the embryo's age. Hit "Calculate Due Date" to instantly see your EDD, current week, trimester, and a full milestone timeline.
Knowing your estimated due date (EDD) is one of the first and most important steps in prenatal care. Your OB-GYN uses it to schedule key screenings — the nuchal translucency scan between weeks 11–14, the anatomy scan around week 20, and glucose tolerance testing around week 24–28. Getting the date right ensures none of these windows are missed.
Consider a real-world example: a woman with a 35-day cycle who uses the standard 28-day formula might miscalculate her EDD by a full week. That seemingly small difference can affect whether a baby is considered premature, full-term, or post-dates — with real clinical consequences. This calculator adjusts for cycle length to give you a more personalized estimate.
Due dates also matter for maternity leave planning, deciding when to share the news (many people wait until after the first trimester ends around week 13), and understanding fetal development milestones. At week 24 the fetus reaches viability; at week 37 it's considered full-term. Knowing where you fall on that timeline helps you have informed conversations with your care team.
The most widely used method is Naegele's Rule, developed in the 19th century and still the clinical standard:
EDD = LMP + 280 days (40 weeks)
This assumes a 28-day cycle with ovulation on day 14. For cycles longer or shorter than 28 days, the formula adjusts:
EDD = LMP + 280 days + (Cycle Length − 28) days
For conception date: EDD = Conception Date + 266 days (38 weeks from fertilization, since pregnancy is measured from LMP which is ~2 weeks before conception).
For IVF: EDD = Transfer Date + (266 − Embryo Age) days. A Day 5 blastocyst transfer adds 261 days; a Day 3 transfer adds 263 days.
The gestational age (how far along you are) is calculated as the number of days elapsed since the LMP equivalent, expressed in weeks and days.
EDDs are estimates, not guarantees. Studies show only about 4–5% of babies are born on their exact due date. However, roughly 80% arrive within 2 weeks of the EDD (between 38–42 weeks). First-trimester ultrasounds are the most accurate method, typically within ±3–5 days.
Use the Conception Date tab if you have a better idea of when you conceived, or the IVF tab if you underwent fertility treatment. Otherwise, your OB-GYN can estimate gestational age via ultrasound measurements — the crown-rump length (CRL) in the first trimester is highly accurate for dating.
Gestational age is counted from the first day of the LMP and is what doctors use — it's about 2 weeks more than the actual fetal age (time since conception). So when your doctor says you're "10 weeks pregnant," your embryo is actually about 8 weeks old. This calculator uses gestational age, which is the standard.
The first trimester runs from week 1 through week 13 (conception through 13 weeks). The second trimester spans weeks 14–26. The third trimester covers weeks 27–40 (or until delivery). Full-term is defined as 39–40 weeks; "early term" is 37–38 weeks and "late term" is 41–42 weeks.