Pregnancy Due Date Calculator
Result Summary
No results yet
Enter your details and hit “Calculate” to see your results.
About the Due Date Calculator
The estimated due date (EDD) anchors all of prenatal care: which week you're in decides when screening tests happen, how growth is judged, and how “early” or “late” is defined at the other end. Obstetrics counts pregnancy as 40 weeks from the last menstrual period — which, counterintuitively, means the clock starts about two weeks before conception.
Pick your best-known starting point. Most people know their last period, so LMP is the default — with a cycle-length adjustment most simple calculators skip. If you know the conception date, or you conceived through IVF (where the embryo's age is known to the day), those are more precise anchors. The result includes how many weeks pregnant you are today and the days remaining.
Tracking a healthy pregnancy week by week? Pair this with the Pregnancy Weight Gain Calculator
The Four Dating Methods
All four methods aim at the same target — 266 days (38 weeks) from conception — they just start counting from different known events:
LMP: due date = last period start + 280 days + (cycle length − 28) Conception: due date = conception date + 266 days IVF day-5: due date = transfer date + 261 days IVF day-3: due date = transfer date + 263 days
| Starting point | Days added | Example (July 1, 2026) | Due date |
|---|---|---|---|
| Last menstrual period (28-day cycle) | 280 | July 1, 2026 | April 7, 2027 |
| Conception date | 266 | July 1, 2026 | March 24, 2027 |
| IVF day-5 embryo transfer | 261 | July 1, 2026 | March 19, 2027 |
| IVF day-3 embryo transfer | 263 | July 1, 2026 | March 21, 2027 |
The old textbook shortcut — Naegele's rule: LMP minus 3 months plus 7 days — approximates the same 280 days and can drift a day depending on month lengths; this calculator counts actual days, per ACOG's definition.
Trimesters at a Glance
Pregnancy is counted in weeks of gestational age (from the LMP-equivalent start). The trimester boundaries this calculator uses:
| Trimester | Weeks | Highlights |
|---|---|---|
| First | 1–13 | Dating ultrasound, first screenings; organs form |
| Second | 14–27 | Anatomy scan (~20 wk); movement felt (~18–22 wk) |
| Third | 28–40+ | Growth checks; full term begins at 37 weeks |
“Full term” spans 39 weeks 0 days to 40 weeks 6 days in ACOG's definitions, with 37–38 weeks called early term and 41+ late term — the due date sits in the middle of a normal range, not at its edge.
How Accurate Are Due Dates?
An EDD is a statistical midpoint, not an appointment: only about 1 in 20 babies arrives on the due date itself, and most arrive within roughly two weeks either side. LMP dating inherits every uncertainty of cycle recall and ovulation timing, which is why ACOG considers a first-trimester ultrasound the most accurate dating method — if an early scan disagrees with your LMP date meaningfully, your provider will re-date the pregnancy to the scan.
Practical reading: treat the due date as the center of a due month. Plan leave, travel, and logistics around weeks 37–42 rather than one calendar day — and let your prenatal care team make the official call, since they'll combine the calendar with ultrasound and exam findings this calculator can't see.
Frequently Asked Questions
How is a due date calculated from my last period?
First day of your last menstrual period + 280 days (40 weeks), per ACOG. If your cycles aren't 28 days, add the difference — a 32-day cycle adds 4 days because ovulation likely happened later. That's the adjustment this calculator applies automatically.
Why does pregnancy count from the last period instead of conception?
Because the period date is known and conception usually isn't. The convention adds the ~2 pre-conception weeks to everyone's count, so “6 weeks pregnant” means about 4 weeks since conception. Every number in prenatal care — screenings, scans, term definitions — uses this LMP-based clock.
How many weeks pregnant am I?
Days elapsed since your LMP-equivalent start ÷ 7. This calculator shows it automatically (e.g., 18 weeks 5 days) along with your trimester. Weeks 1–13 are the first trimester, 14–27 the second, 28 onward the third.
Can my due date change?
Yes — most commonly after a first-trimester ultrasound, which ACOG regards as the most accurate dating tool. If the scan's estimate differs enough from your LMP date, your provider re-dates the pregnancy. After that, the date normally stays fixed even if later scans measure big or small.
What are the chances of delivering on my due date?
Around 1 in 20. The due date is the middle of a distribution: full term runs 37–42 weeks, and first babies statistically run slightly later. Think “due month,” not due day.
How does IVF due-date math differ?
IVF removes the guesswork — the embryo's age is known exactly. A day-5 blastocyst transfer adds 261 days to the transfer date (280 − 14 ovulation-equivalent − 5 embryo days); a day-3 transfer adds 263. No cycle-length adjustment is needed.
Sources & References
- [1](2017). Methods for Estimating the Due Date (Committee Opinion No. 700) — American College of Obstetricians and Gynecologists (ACOG)
Methodology. This calculator uses formulas and health categories recognized by the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC). It is reviewed and maintained by the Vast Calculators editorial team.
Last updated · July 2026
Disclaimer. This tool provides estimates for general informational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare provider before making decisions about your health.