Pregnancy Due Date Calculator

About this calculator

This calculator estimates when your baby is likely to arrive based on your last menstrual period, conception date, or IVF embryo transfer. It also shows your current gestational age in weeks and days, and which trimester you are in. The result is an estimate — only about 4% of births happen on the exact due date — and it is not a substitute for prenatal care.

How to read your results

The headline is your estimated due date (EDD). Below it you will see your gestational age (weeks + days since your last menstrual period) and your trimester. The 40-week timeline bar shows where you are in the pregnancy, with the three trimester segments clearly marked. Use the result as a planning guide, not a guarantee.

How it's calculated

For the LMP method the calculator applies Naegele's rule: EDD = LMP + 280 days + (cycle length − 28 days). The extra term adjusts for cycles that differ from the assumed 28-day average — a 30-day cycle shifts the EDD two days later, a 26-day cycle two days earlier. For a conception date the formula is EDD = conception + 266 days (equivalent to LMP + 280 when ovulation occurs at day 14). IVF 5-day transfer uses EDD = transfer + 261 days; IVF 3-day transfer uses EDD = transfer + 263 days. Gestational age is the number of days between the effective LMP and the reference date, expressed as weeks and remainder days. Trimesters follow the boundaries used by ACOG (American College of Obstetricians and Gynecologists).

Worked example

Last menstrual period: 15 January 2026; cycle length: 28 days. Today: 1 May 2026.

Estimated due date: 22 October 2026. On 1 May 2026 you would be 15 weeks and 1 day along, in the second trimester.

Frequently asked questions

What is Naegele's rule?

Naegele's rule is the standard method for estimating a due date: add 280 days (40 weeks) to the first day of your last menstrual period, assuming a 28-day cycle. If your cycle is longer or shorter, the calculator adjusts by the difference in days.

How accurate is the due date?

An LMP-based estimate is typically accurate to within about one week. An early ultrasound (before 14 weeks) is more precise and is used by clinicians to confirm or revise the due date. Only around 4% of babies are born on their exact due date; most arrive within two weeks either side.

What if I know my conception date or had IVF?

Select the matching method. A conception date produces the same EDD as an LMP estimate shifted 14 days back. For IVF, use the 5-day blastocyst transfer option (adds 261 days) or the 3-day embryo transfer option (adds 263 days) — these account for the fact that the embryo is already a few days old at transfer.

What do the trimesters mean?

The first trimester runs from conception through 13 weeks and 6 days (97 gestational days). The second trimester covers weeks 14 through 27 (days 98–195). The third trimester begins at week 28 and ends at birth. Key milestones are foetal viability around 24 weeks and full term at 37 weeks.

Is this medical advice?

No. This tool provides an informational estimate only. Always confirm your due date with a healthcare professional and follow their guidance for prenatal care.

Sources

• www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/05/methods-for-estimating-the-due-date
• www.nhs.uk/pregnancy/finding-out/due-date

Reviewed by the YouCalc Team · Last reviewedJune 11, 2026