Due Date Calculator (from Conception Date)
Estimate the expected due date and current gestational age from a known or estimated conception date — useful when LMP is unknown or assisted reproduction was used.
Per Naegele's Rule (LMP + 280 d) and ACOG Committee Opinion 700 (reaffirmed 2024). First-trimester ultrasound CRL is the most accurate single dating method and overrides LMP-based EDD if >7 days off. Term ranges per ACOG 2013: early 37+0–38+6, full 39+0–40+6, late 41+0–41+6, post-term ≥ 42+0. ~85% of singleton births fall 37+0–41+6.
General calculation reads
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About this tool
The standard obstetric due date (estimated date of delivery, EDD) is 280 days from the first day of the last menstrual period (LMP) per Naegele's Rule. Because conception typically occurs around cycle day 14 (ovulation), the conception-based equivalent is 266 days from conception, or 38 weeks. This calculator is most accurate when conception date is known precisely — usually after IVF embryo transfer (add 38 weeks − embryo age) or with ovulation tracking via LH urine tests or basal body temperature charting. For natural cycles with unknown ovulation, the LMP method is more reliable. ACOG Committee Opinion 700 (reaffirmed 2024) notes that first-trimester ultrasound dating (crown-rump length) is the most accurate single dating method and overrides LMP-based EDD if the difference exceeds 7 days in the first trimester. Only about 4–5% of births occur on the exact EDD; the standard term range (37+0 to 41+6 weeks) covers ~85% of singleton deliveries.
How to use it
- Enter the conception date (IVF transfer date or ovulation date).
- For IVF: pick the embryo age (day 3 or day 5 blastocyst).
- Read your EDD (280-day LMP equivalent and 266-day conception equivalent), current gestational age, and trimester.
- For natural conception with unknown ovulation, use the LMP-based calculator instead.
Frequently asked questions
- Why two due dates?
- The 266-day conception EDD reflects actual fetal age. The 280-day LMP EDD is the convention used in all OB practice and on ultrasounds because LMP is what is recorded. They differ by 14 days.
- IVF transfer day 3 vs day 5?
- A day-3 embryo is 3 days old at transfer; a day-5 blastocyst is 5 days old. Adjust EDD = transfer date + (266 − embryo age) days. This calculator does the math for you.
- How accurate is this?
- Conception date ± 1 day is more accurate than LMP-based dating (typical SD ≈ 8 days). First-trimester ultrasound (CRL measurement) is most accurate of all per ACOG.
- What defines term?
- Per ACOG 2013: early term 37+0 to 38+6, full term 39+0 to 40+6, late term 41+0 to 41+6, post-term ≥ 42+0 weeks. ~85% of births fall in the 37+0–41+6 range.
- Is data sent anywhere?
- No. All math runs in your browser.