Due Date Calculator
Estimate your pregnancy due date four ways: from your last menstrual period, a known conception date, an IVF embryo transfer, or an early ultrasound. You will also see how many weeks along you are today, your current trimester, an estimated conception date, and a timeline of the milestones ahead.
Formula
Worked example
Last period starting 1 Nov 2025 with a 28-day cycle gives a due date of 8 Aug 2026 (280 days later) and conception around 15 Nov 2025. A Day 5 IVF embryo transferred 15 Nov 2025 adds 261 days for the same 3 Aug 2026 window.
Four ways to estimate a due date
This calculator supports the four dating methods used in clinics. The last menstrual period (LMP) method adds 280 days (40 weeks) to the first day of your last period and adjusts for your cycle length. The conception method adds 266 days, since pregnancy lasts about 38 weeks from fertilisation. The IVF method uses the transfer date and the embryo age: a Day 5 blastocyst is already five days past fertilisation, so it adds 261 days (266 minus 5), a Day 3 embryo adds 263 days, and a Day 6 adds 260. The ultrasound method takes the gestational age your scan measured and projects forward to 40 weeks. Internally, every method is converted to one effective last-period date so the result stays consistent however you enter it.
How far along you are, and the milestone timeline
Pregnancy is divided into three trimesters: the first runs through week 13, the second from weeks 14 to 27, and the third from week 28 until birth. The gauge marks where you are on the 40-week journey based on today, and the calculator shows how many days remain (or how many days overdue you are). The milestone timeline lists the dates for the key moments ahead, the dating scan, the 20-week anomaly scan, the start of full term at 37 weeks, your due date at 40 weeks, and the post-term point at 42 weeks, all calculated from your effective last-period date. A full-term birth is anywhere from 37 to 42 weeks, so the due date is a midpoint, not a deadline.
Why an ultrasound may give a different date
LMP dating assumes a regular cycle and ovulation around day 14. If your cycle is irregular or you are unsure of your LMP, an early dating ultrasound that measures the baby is more accurate and may move your due date by several days. IVF dating is also precise because the exact day of fertilisation is known. Healthcare providers generally use the ultrasound date when it differs significantly from the LMP estimate, so treat this as a planning figure to confirm at your first appointment.
Frequently asked questions
How accurate is a due date?
It is an estimate. Only around 4 to 5% of babies are born on their exact due date; most arrive within the two weeks before or after. An early ultrasound or IVF dating improves accuracy, particularly for irregular cycles.
How do I calculate a due date from an IVF transfer?
Start from the transfer date and add 266 days minus the embryo age. A Day 5 blastocyst adds 261 days, a Day 3 embryo adds 263 days, and a Day 6 adds 260 days. Choose the IVF method above and the calculator does this for you, including a frozen embryo transfer (FET).
Why does pregnancy count from my last period?
Dating from the last menstrual period gives a consistent, knowable starting point, since the exact day of conception is usually uncertain. This is why you are considered about two weeks pregnant at the moment of conception, and why all four methods here are converted to that same effective last-period date.
What if my cycle is not 28 days?
Use the LMP method and enter your average cycle length. The calculator shifts the due date accordingly, because ovulation, and therefore conception, happens later in a longer cycle and earlier in a shorter one.