Pregnancy Due Date Calculator
Estimate a pregnancy due date using Naegele's rule (LMP + 280 days), a known conception date, or an IVF embryo transfer date — plus current gestational age, trimester, and the start of each trimester. For informational use only, not medical advice.
Input
The first day of your last menstrual period.
Average length of your menstrual cycle. Longer or shorter cycles shift the estimated due date.
Leave blank to use today's date. Set an exact date for reproducible gestational age and trimester results.
Output
| Metric | Value |
|---|---|
| No data yet | |
Guides
The Pregnancy Due Date Calculator estimates a baby's due date (EDD) from the first day of your last menstrual period, a known conception date, or an IVF embryo transfer date. It also reports your current gestational age, trimester, and the dates each trimester begins.
This tool provides an estimate for informational purposes only — it is not medical advice. Only about 5% of babies are born exactly on their due date; most arrive within two weeks before or after. Always confirm dates and milestones with your healthcare provider.
How it works
The default method uses Naegele's rule: the due date is set 280 days (40 weeks) after the first day of the last menstrual period (LMP). Because Naegele's rule assumes a textbook 28-day cycle with ovulation on day 14, the calculator lets you adjust for a longer or shorter average cycle length — a longer cycle ovulates later, so the effective LMP (and the due date) shifts forward, and a shorter cycle shifts it back.
If you know your conception date more precisely (for example, from ovulation tracking), you can calculate from that instead — the due date is set 266 days (280 − 14) after conception. For IVF pregnancies, select the embryo transfer date and the embryo's age at transfer (a Day 3 embryo or a Day 5 blastocyst); the calculator backs out an equivalent LMP by subtracting 14 days plus the embryo's age from the transfer date.
How to use it
- Choose a Calculation Method: Last Menstrual Period, Conception Date, or IVF Transfer Date.
- Enter the date the chosen method needs (and, for LMP, your average cycle length; for IVF, the embryo's age at transfer).
- Optionally set an As of Date — the date to measure gestational age and trimester against. Leave it blank to use today's date.
- The results update automatically and include:
- Estimated Due Date — the calculated EDD
- Estimated LMP and Estimated Conception Date — the anchor dates every other figure is derived from
- Gestational Age — weeks and days pregnant as of the reference date
- Trimester — 1st (weeks 1–13), 2nd (weeks 14–27), or 3rd (weeks 28–40)
- Days Until Due Date (or Days Since Due Date, if the due date has passed)
- End of 1st Trimester, End of 2nd Trimester, and Full Term Begins (week 37) — key milestone dates
Results can be copied or downloaded as a CSV file.
FAQ
How accurate is Naegele's rule?
Naegele's rule is a widely used estimate, not a guarantee — actual gestation length varies naturally by more than two weeks even for a healthy, full-term pregnancy. It also assumes a regular 28-day cycle with ovulation on day 14; the cycle-length adjustment here corrects for that assumption, but an ultrasound dating scan in the first trimester is generally considered the most accurate way to confirm a due date.
Why does the conception-date method subtract 266 days differently from the LMP method's 280?
They land on the same due date for a textbook cycle: conception typically occurs about 14 days after the LMP, so LMP + 280 days equals conception + 266 days. The calculator actually derives an "estimated LMP" from whichever date you provide (conception − 14 days, or transfer date − 14 days − embryo age), then applies the same 280-day rule from that point — which is why every method's output includes an "Estimated LMP" row even if you never entered one directly.
What do "Day 3 Embryo" and "Day 5 Blastocyst" mean for the IVF method?
They describe how many days the embryo was cultured before transfer. A Day 5 blastocyst transfer is equivalent to a natural conception 5 days earlier than a Day 3 transfer, so the calculator subtracts a different offset (14 + 5 = 19 days for a blastocyst, 14 + 3 = 17 days for a Day 3 embryo) from the transfer date to back out the estimated LMP.
Why does gestational age show "Not yet pregnant on this date"?
This appears when the "As of Date" falls before the estimated conception date implied by your inputs — for example, if you set a reference date earlier than the LMP-derived conception date. It's a sign the reference date and the pregnancy dates don't overlap, not an error in the calculation.
Is my data sent anywhere?
No. All dates are processed entirely in your browser — nothing is uploaded or stored, and the calculation works the same way offline.