Pregnancy Due Date Calculator
Enter your last period, conception date, or IVF transfer date to see your estimated due date, current gestational age, and trimester milestones.
Estimate only — not medical advice. Every pregnancy is different; confirm your due date and care plan with a doctor or midwife.
The first day of bleeding, not the day it ended.
From the first day of one period to the first day of the next. 28 days is the default; most cycles run 21–45 days.
The estimated date of conception or ovulation, for example from an ovulation test or fertility tracking.
The date of your embryo transfer — this can be a past or a scheduled future date.
Trimester milestones
Calculated in your browser. Your dates stay on this device and are never sent to a server.
Understanding your estimated due date
A due date marks 40 completed weeks of pregnancy, yet a pregnancy that reaches its due date has actually been developing for about 38 weeks — the count starts roughly two weeks before conception. This estimated due date (EDD) gives you and your care team a shared reference for scheduling scans, screening tests, and routine appointments. It is a planning anchor, not a delivery appointment: births cluster around the date rather than land on it.
This calculator offers three starting points because different pregnancies are dated differently. If you know the first day of your last menstrual period (LMP), it uses the calendar method. If you tracked ovulation or know your conception date, it counts forward from there. If you conceived through IVF, it uses the known embryo age at transfer, usually the most precise of the three inputs.
How each method is calculated
The LMP method follows Naegele's rule: add 280 days (40 weeks) to the first day of your last period, assuming ovulation around day 14 of a 28-day cycle. If your typical cycle is longer or shorter, the calculator shifts the estimate by the difference from 28 days, because a longer cycle means later ovulation. The conception method adds 266 days to the date of ovulation. The IVF method adds 261 days for a day-5 blastocyst transfer, or 263 days for a day-3 cleavage-stage transfer.
Reading gestational age and trimesters
Gestational age is reported in completed weeks and days from the LMP — "14 weeks 2 days" means 14 full weeks plus 2 days. Clinicians divide the roughly 40 weeks into three trimesters, though exact boundaries vary slightly between sources. The table shows the convention this tool uses.
| Stage | Gestational weeks | Typical milestones |
|---|---|---|
| First trimester | Weeks 1–13 | Organs form; early ultrasound dating |
| Second trimester | Weeks 14–27 | Anatomy scan; first movements felt |
| Third trimester | Weeks 28–40+ | Rapid growth; term from week 37 |
| Full term | Weeks 37–42 | Normal delivery window |
Common misunderstandings
- Only about 1 in 20 babies arrive on the due date. Most are born within the two weeks on either side, and anything from 37 to 42 weeks is full term.
- Week 4 does not mean a four-week-old embryo. Because dating starts at the LMP, the embryo is about two weeks younger than the gestational age suggests.
- Irregular cycles reduce LMP accuracy. If your cycles vary a lot, an early ultrasound is generally the more reliable way to date the pregnancy.
Limits — and a note on medical advice
This tool is an estimate only and is not medical advice. It cannot account for early-ultrasound redating, multiple pregnancies, or individual health factors, and it does not diagnose anything or recommend care. Every pregnancy is different: use the date to plan and prepare, but confirm your dating and any decisions with a doctor or midwife who can assess your specific situation.
Sources & further reading
Frequently asked questions
How is my pregnancy due date calculated from my last period?
Most due date calculators use Naegele's rule: count 280 days (40 weeks) from the first day of your last menstrual period (LMP), assuming a standard 28-day cycle where ovulation happens around day 14. For example, an LMP of January 1 gives an estimated due date around October 8. If your average cycle is longer or shorter than 28 days, this pregnancy calculator shifts the estimate by the difference — a 32-day cycle pushes ovulation, and the due date, about 4 days later; a 24-day cycle about 4 days earlier.
How accurate is a due date, and how many babies are born on it?
A due date is a statistical estimate, not a prediction of the exact day. Only around 1 in 20 babies are born on their estimated due date; most arrive within the two weeks before or after it, and a full-term pregnancy is considered anywhere from 37 to 42 weeks. First-trimester ultrasound dating is generally considered more accurate than a calculation from your last period alone, especially if your cycles are irregular, so treat this calculator's date as a helpful planning estimate rather than a guarantee.
How does an IVF transfer date change the due date calculation?
IVF due dates are calculated from the embryo's known age at transfer rather than from a last period, which is why they tend to be more precise. For a day-3 (cleavage-stage) transfer, this calculator adds 263 days to the transfer date; for a day-5 (blastocyst) transfer, it adds 261 days. Both formulas assume the embryo reached day 3 or day 5 at the same pace a standard 28-day cycle would put ovulation on day 14, so the due date lands 40 weeks after that equivalent starting point.
What is gestational age, and why does it start before conception actually happens?
Gestational age is the medical convention for how far along a pregnancy is, and by tradition it is counted from the first day of the last menstrual period — about two weeks before ovulation and conception typically occur. So in week 4 of a pregnancy, the embryo itself is usually only about 2 weeks old. This calculator reports gestational age in completed weeks and days using that same convention, whichever method (LMP, conception date, or IVF transfer) you use to estimate it.
Is my due date or personal date information sent to a server?
No. Every calculation in this pregnancy due date calculator runs locally in your browser using JavaScript. Your last period date, conception date, or transfer date is saved only in this browser's local storage so the form is ready next time you visit, and "Clear saved dates" removes it immediately. Nothing is uploaded, there is no account, and no one else can see what you entered.