📅 Due Date Calculator
When the conception date is known — or an IVF transfer date is on record — dating a pregnancy gets more precise than the period-based estimate. Human gestation averages 266 days from conception.
For IVF, a day-3 embryo is about 3 days post-fertilization and a day-5 blastocyst about 5 days, so the calculator counts back accordingly.
How to use this calculator
Tell the tool whether you know a conception date or an IVF transfer date, enter that date, and it estimates your baby's due date.
- Use the Known date is dropdown to pick Conception date or an IVF transfer option.
- Enter the Date in the date field.
- Read your Estimated due date in the results.
- For IVF, notice the tool adjusts automatically for day-3 embryos or day-5 blastocysts.
Frequently asked questions
What does this due date calculator compute and what are the inputs?
It estimates your delivery date from a known starting point instead of a last period. You pick whether that starting point is a conception date, a day-3 embryo transfer or a day-5 blastocyst transfer, then enter the date.
How does the calculation work?
It adds 266 days, the average human gestation from conception, to the given date. For IVF transfers it first shifts the date back by the embryo's age (3 or 5 days) so the 266-day count still starts at fertilisation.
Can you show a worked example?
A day-5 blastocyst transferred on 2026-08-18 counts as conception on 2026-08-13, and adding 266 days gives an estimated due date of 2027-05-06. With a natural conception date of 2026-07-13 the same maths gives 2027-04-05.
Is this more accurate than the period-based due date?
Yes, when the conception or transfer date is genuinely known, because it skips the guesswork about ovulation timing. Even so, babies rarely arrive exactly on time, so keep it as an estimate and confirm with your healthcare provider.