Free Pregnancy Due Date Calculator
Estimate a due date from the last menstrual period, conception or IVF transfer, with gestational age on a chosen date. Use advanced options and copy or download your results. Browser-based and no signup required.
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How to use the pregnancy due date calculator
Estimate a due date from the last menstrual period, conception or IVF transfer, with gestational age on a chosen date. No signup required.
- Choose dating from the last menstrual period, a known conception date or an IVF embryo transfer.
- Enter the matching source date. For LMP, set usual cycle length; for IVF, enter embryo age at transfer.
- Choose a reference date for the estimated gestational age and days remaining.
- Review the estimated due date and consult your maternity clinician about clinical dating before using it for care decisions.
When a due date estimate helps
After a positive test, many people want a rough idea of when the baby may arrive. A due date estimate helps with practical planning, such as telling family, arranging time off work or thinking about the first prenatal visit. Partners and relatives also use it to follow along week by week.
The calculator suits three situations. Most people date a pregnancy from the first day of the last menstrual period. Some know the conception date, for example from ovulation tracking. Those who conceived through IVF know the exact transfer date and embryo age. Your clinician will set the official date, but a home estimate gives you a starting point.
A worked example with real dates
Suppose the last period began on January 10, 2026, and the usual cycle is 30 days. The formula is first day plus 280 days plus the cycle length minus 28. That is January 10 plus 282 days, which gives an estimated due date of October 19, 2026.
Now set the reference date to April 15, 2026. There are 187 days from April 15 to October 19. Gestational age is 280 minus 187, which is 93 days, shown as 13 weeks 2 days. The days remaining line would show 187.
For IVF, take a transfer on March 2, 2026, with a five-day embryo. The formula is transfer date plus 266 days minus 5, so March 2 plus 261 days, which is November 18, 2026.
How the dating methods work
The standard rule counts 40 weeks, or 280 days, from the first day of the last period. This assumes a 28-day cycle with ovulation around day 14. A longer cycle usually means later ovulation, so the calculator adds the extra days. A 32-day cycle adds 4 days, while a 25-day cycle subtracts 3. Cycle length can be set from 21 to 40 days.
Conception dating adds 266 days, since conception is assumed to occur about two weeks after the period started. IVF dating also starts from 266 days but subtracts the embryo's age at transfer, from 3 to 6 days. Gestational age is always counted back from the due date, so it is shown in the usual weeks plus days format used by clinics.
Common mistakes to avoid
A frequent error is entering the date the period ended instead of the date it started. Another is using an average cycle length when cycles vary widely. Both shift the estimate by days or more. If your cycles are irregular, the result is less reliable, and an early ultrasound is the usual way to date the pregnancy.
Also avoid treating the due date as a deadline. Only a small share of babies arrive on the exact day, and a full-term birth can happen in the weeks before or after it. This tool gives general information only. Discuss your dates, and any decisions about care, with a doctor or midwife.
Useful tips and limitations
- The LMP method adds 280 days with a simple cycle-length adjustment; irregular cycles reduce reliability.
- Early ultrasound and clinical history can revise an estimated due date. The result is not a promised birth date.
- Write down the first day of each period in a calendar or app, because an exact start date makes the estimate more accurate.
- Change the reference date to a future appointment to see how far along the pregnancy will be on that day.
Common questions
Does this due date calculator always add exactly 40 weeks?
The LMP method adds 280 days plus the entered cycle length minus 28 days. Conception uses 266 days, while IVF transfer uses 266 days minus embryo age.
Can I calculate a due date after IVF transfer?
Yes. Choose IVF, enter the transfer date and the embryo age in days at transfer. Your fertility or maternity clinician should confirm the clinical estimated due date.
Why might a clinician change the calculated pregnancy date?
LMP recall, irregular cycles, variable ovulation and ultrasound findings can affect dating. This calendar estimate cannot replace clinical pregnancy dating.
Why does the calculator ask for embryo age with IVF?
A day-5 embryo is already five days past fertilization when it is transferred. Subtracting that age from 266 days lines the estimate up with standard gestational dating.
What does Outside the usual gestation range mean?
It appears when the reference date is before the pregnancy start or more than 44 weeks along. Check the dates you entered.
Does a shorter cycle move my due date earlier?
Yes, in the LMP method. Each day the cycle is shorter than 28 moves the estimate one day earlier, because ovulation is assumed to happen sooner.
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