From your last period (LMP)
We add 280 days (40 weeks) to the first day of your last menstrual period. If your cycle is longer or shorter than 28 days, we shift the due date by the same number of days.
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Pregnancy Due Date Calculator
Enter your last period, conception date, or IVF transfer to get your estimated due date, plus current week, trimester, and how many days are left.
✻ Naegele's ruleAdjusts for cycle lengthSupports IVF dates
Average is 28. Longer cycles push the due date later.
How the calculation works
From the conception date
If you know exactly when you conceived, through ovulation tracking or fertility treatment, we add 266 days (38 weeks) directly. This skips the cycle-length guesswork entirely.
From an IVF transfer
For a Day-5 blastocyst transfer, due date = transfer date + 261 days. For a Day-3 embryo, transfer date + 263 days. Embryo age replaces the LMP-to-ovulation estimate.
Frequently asked questions
How accurate is a due date calculator?
Calendar-based due dates assume a 28-day cycle and ovulation on day 14. About 5% of babies arrive on the predicted date, most are born within two weeks on either side of it. Early ultrasounds (before week 13) give the most reliable date, since fetal size at that point is consistent across pregnancies.
What is Naegele's rule?
Naegele's rule is the standard formula: take the first day of your last menstrual period, subtract 3 months, and add 7 days. That equals 280 days (40 weeks) of pregnancy. This calculator does the same math but adjusts for cycle length and IVF transfer dates.
Why does cycle length matter?
Naegele's rule assumes a 28-day cycle with ovulation around day 14. If your cycles run 32 days, you typically ovulate around day 18, meaning conception happens four days later than the formula assumes, and your due date shifts four days later too.
How is the IVF due date calculated differently?
IVF removes the guesswork about ovulation. For a Day-5 embryo (blastocyst) transfer, due date = transfer date + 261 days. For a Day-3 embryo, it's transfer date + 263 days. Frozen-embryo transfer (FET) follows the same rule.
When should I see a healthcare provider?
If you've had a positive home pregnancy test, schedule a first prenatal visit within the first 8 weeks. Your provider will confirm the due date with an early ultrasound, screen for risk factors, and start prenatal vitamins if you're not already taking them.
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