Estimate a due date from your last period, known conception date or IVF embryo transfer, then review pregnancy week, trimester and milestone dates.
Pregnancy & fertility calculator
Use a last period, conception date or day-3/day-5 embryo transfer and see pregnancy progress plus milestone dates.
Your entries stay in this browser and are only used for this calculation.
Estimated due date
Your estimated due date, pregnancy week, due window and milestone schedule will appear here.
Methodology
LMP mode adds 280 days and adjusts for the difference between the entered cycle length and 28 days. Conception mode adds 266 days. Following ACOG examples, day-3 and day-5 IVF transfer modes add 263 and 261 days respectively. Pregnancy progress is counted from the equivalent LMP date.
Worked example
For an LMP of January 1 with a 28-day cycle, the estimated due date is October 8. A conception date of January 15, a day-3 transfer on January 18 or a day-5 transfer on January 20 produces the same estimated due date.
Four dating methods
A remembered LMP is useful when cycles are regular. A known fertilization date removes some uncertainty, while assisted-reproduction dating uses the embryo age and transfer date. The calculator keeps those methods separate instead of treating every entered date as an LMP.
If an early ultrasound or fertility clinic has already established the pregnancy date, that documented estimate takes priority over a new calendar calculation.
Official reference
The American College of Obstetricians and Gynecologists explains that pregnancy averages 280 days, or 40 weeks, when counted from the first day of the LMP. Its clinical guidance also gives embryo-transfer examples for IVF dating.
ACOG: understanding the estimated due dateRelated pregnancy tools
Common questions
The standard estimate adds 280 days to the first day of the last menstrual period. This calculator also adjusts that estimate when you enter a cycle length other than 28 days.
ACOG describes adding 263 days to a day-3 embryo transfer or 261 days to a day-5 transfer. IVF dating should ultimately follow the dates documented by the fertility clinic.
No. It is an estimated date used to organize pregnancy care. Labor can begin before or after that date, so the result also shows a two-week window on either side.
LMP dating assumes the period date and ovulation timing are reliable. Early ultrasound measurements may support a different obstetric estimate, particularly when periods are irregular or the LMP is uncertain.
It can affect a calendar estimate. A longer cycle may imply later ovulation and a shorter cycle may imply earlier ovulation, but individual cycles vary and the adjustment is still only an estimate.
No. Once a care professional establishes the best obstetric due date, online calculations should not replace it. Use this result to understand the dates, then follow the clinical record.
Every date is an estimate. LMP calculations depend on recall and cycle timing, while IVF calculations depend on the documented transfer date and embryo age. Use the due date established by your obstetric or fertility care team for medical decisions and appointment scheduling.