Pregnancy Due Date Calculator
Estimate your due date from the first day of your last period, a known conception date, an IVF transfer date, or ultrasound dating — plus how far along you are.
Pregnancy tracking apps and resources
Learn moreHow the date is estimated
The standard estimate, Naegele’s rule, adds 280 days (40 weeks) to the first day of your last period. It assumes a 28-day cycle and ovulation around day 14, so a longer or shorter cycle shifts the date. Only about 1 in 20 babies actually arrives on the due date — it’s a center point, not a deadline. If you know your conception date, IVF transfer date, or an ultrasound’s dating measurement, those methods can be more precise than counting from your last period — switch dating methods above to use whichever date you know.
How it’s calculated & sources
Last period (Naegele’s rule): due date = last period + 280 days, adjusted for cycle length (days beyond 28 push it later). Estimated conception is ~14 days after the last period. Conception date: due date = conception date + 266 days (38 weeks), since a due date sits at 280 days from LMP, or 266 days from conception. IVF transfer: due date = transfer date + 263 days for a day-3 transfer, or + 261 days for a day-5 (blastocyst) transfer — both anchored to 266 days from fertilization minus the embryo’s age at transfer. Ultrasound dating: due date = ultrasound date + (280 − gestational age measured at the scan, in days). Current week counts from the last period, conception date, or the equivalent gestational start date implied by the IVF or ultrasound inputs, depending on the selected method.
Benchmark: Naegele’s rule (last menstrual period + 280 days) plus the conception-date, IVF-transfer, and ultrasound-dating methods — the standard obstetric dating approaches.
Results update as you type and are general estimates, not personalized financial, tax, medical or legal advice. Verify with a professional.
Worked example
A last period on January 1 with a 28-day cycle gives a due date around October 8, with conception estimated in mid-January. Using the other methods: a known conception date of January 15 gives a due date around October 8 as well (conception + 266 days); a day-5 embryo transfer on January 20 gives a due date around October 8 (transfer + 261 days); and an ultrasound on February 26 measuring 8 weeks 0 days of gestational age gives a due date around October 8 (scan + 224 remaining days) — all four methods converge on the same date when the underlying pregnancy timing is consistent.
Frequently asked questions
How accurate is the due date?
It’s an estimate — a normal birth can occur up to two weeks either side. An early ultrasound often refines the date.
What if my cycle isn’t 28 days?
Enter your cycle length and the tool shifts the date accordingly, since ovulation timing moves with cycle length.
Which dating method should I use?
Use whichever date you know most precisely. IVF transfer dates are the most exact since the embryo’s age is known; an early ultrasound is the next most reliable; a known conception date is very accurate; last-period (LMP) dating is the most common starting point but assumes a textbook 28-day cycle.
How does the IVF due date calculation work?
Due date is estimated as 266 days after conception/fertilization (the same point IVF timing is anchored to). For a day-3 transfer the embryo is already 3 days old, so the due date is the transfer date plus 263 days; for a day-5 blastocyst transfer it’s the transfer date plus 261 days.
How does ultrasound dating work?
You enter the scan date and the gestational age the ultrasound measured at that time. The due date is set at 280 days of total gestation, so we add the remaining days (280 minus the age already measured) to the scan date. Early first-trimester scans are the most accurate for dating.