Pregnancy Due Date Calculator
Get your estimated due date (EDD) instantly from your LMP, conception date, IVF transfer, or early ultrasound
Last updated: October 23, 2026 · Methods checked against ACOG dating standards
Why Calculate Your Due Date Early?
The moment a pregnancy test turns positive, one question beats all the rest: “When is my baby due?” Your estimated due date (EDD) is the anchor for your entire pregnancy — it tells you how many weeks pregnant you are, which trimester you are in, when prenatal screenings are scheduled, and roughly when to expect labor. Enter the first day of your last period and your average cycle length, and our calculator applies the same standard dating rules (Naegele’s rule) that OB/GYNs use.
No matter how you track your pregnancy — a regular or irregular cycle, IVF or frozen embryo transfer, a known conception date, or early ultrasound measurements — this tool has a method for you, and it builds your complete trimester timeline in seconds.
How Your Due Date Is Calculated
Four medically accepted methods — pick the one that fits your pregnancy
Last Menstrual Period (Naegele's Rule)
Add 280 days (40 weeks) to the first day of your last period, then adjust for cycles longer or shorter than 28 days. The classic method, dating back to 1812.
Use this calculator →Conception or Ovulation Date
If you tracked ovulation or know when you conceived, add 266 days (38 weeks). Best accuracy when conception day is known precisely.
Use this calculator →IVF / Embryo Transfer
Add 266 days minus the embryo's age at transfer. Day 3: +263 days. Day 5 blastocyst: +261 days. The most precise dating method available.
Use this calculator →Ultrasound (CRL Dating)
A first-trimester ultrasound measures crown-rump length to date the pregnancy within ±5 days — the gold standard doctors use to confirm or correct LMP dates.
Use this calculator →How Accurate Is a Due Date, Really?
The honest numbers every expecting parent should know
A due date is an estimate, not an appointment — think of it as the center of your most-likely delivery window. That is why providers confirm it with an early ultrasound and rarely change it afterward. The American College of Obstetricians and Gynecologists (ACOG) advises redating only when a first-trimester scan disagrees with LMP dating by more than 5 days up to 8 weeks 6 days, or more than 7 days between 9 weeks 0 days and 13 weeks 6 days. Read the plain-language guide →
Due Date Methods Compared: Formula, Accuracy & Best Use
Every method targets the same 40-week finish line — what differs is the starting event and the margin of error
| Method | Formula | Typical accuracy | Best for |
|---|---|---|---|
| Last menstrual period (LMP) | LMP + 280 days ± (cycle − 28) | Within ~1 week with regular cycles | Most pregnancies, first estimate |
| Conception / ovulation date | Conception + 266 days | Within a few days if ovulation is tracked | Irregular cycles, tracked ovulation |
| IVF embryo transfer | Day 3: +263 days · Day 5: +261 days | Most precise — embryo age is known exactly | IVF and frozen embryo transfers |
| First-trimester ultrasound (CRL) | Scan date + (280 − gestational age in days) | ±5–7 days up to 13 weeks 6 days | Confirming or correcting any date |
| Second-trimester ultrasound | Biometry (head, abdomen, femur) | ±7–14 days | Late first visit to care |
| Third-trimester ultrasound | Biometry (growth measurement) | ±21–30 days — not used for dating | Growth monitoring only |
The ranking is consistent across clinical guidance: a known embryo transfer date and a first-trimester crown-rump length (CRL) measurement are the most precise anchors, while LMP dating is the practical starting point that an early scan then verifies. Whichever method you start with, the earliest reliable measurement is the one your provider will keep for the rest of the pregnancy.
Pregnancy Week by Week: Baby Development & Symptoms
Click your week for baby’s size, development milestones, symptoms, and checklists — all 42 weeks
Explore Pregnancy by Trimester
From conception to a fully formed fetus — organ formation, morning sickness, first prenatal visits, and screening tests.
The golden period — energy returns, first kicks arrive, the anatomy scan reveals your baby in detail.
The home stretch — rapid weight gain, kick counts, birth planning, and recognizing the signs of labor.
Why Parents Choose Our Due Date Calculator
Doctor-grade dating formulas, zero hassle
Instant Results
Enter your LMP and cycle length — see your due date, current week, trimester, and milestones in under 3 seconds.
Doctor-Grade Formulas
Built on Naegele's rule, IVF transfer protocols, and CRL ultrasound dating — the same methods OB/GYNs use worldwide.
Full Pregnancy Dashboard
Not just a date: get your trimester dates, week-by-week development, prenatal test windows, and countdown.
Works for Every Pregnancy
Irregular cycles, IVF and frozen embryo transfers, known conception dates, and ultrasound measurements — all supported.
Free & 100% Private
No sign-up, no fees, no data collection. Everything is calculated instantly in your own browser.
Perfect on Mobile
Fully optimized for phones, tablets, and desktops — check your dates anytime, anywhere.
More Pregnancy & Fertility Calculators
Sources and References
- American College of Obstetricians and Gynecologists (ACOG). Methods for Estimating the Due Date. Committee Opinion No. 700 — the clinical standard for LMP, ultrasound, and ART due-date methods and redating thresholds. acog.org — Committee Opinion No. 700
- NHS. Due date calculator — the UK health service’s LMP-based due date method and pregnancy guidance. nhs.uk — Due Date Calculator
- Johns Hopkins Medicine. Calculating a Due Date — patient guidance on Naegele’s rule and ultrasound confirmation. hopkinsmedicine.org — Calculating a Due Date
All dating methods on this page follow the conventions above. Last reviewed October 23, 2026.
Frequently Asked Questions About Pregnancy Calculators
Common questions answered by our medical team