Pregnancy Due Date Calculator
Estimated due date, conception date, current week and trimester milestones.
What it does
Estimates the due date, conception date, current week and trimester from the last period, the conception date or an IVF transfer date.
Where it's used
Planning appointments and following a pregnancy week by week.
How to use it
- Choose what date you know.
- Pick the date.
- For the last period, enter your average cycle length.
- Read the due date, current week and milestones.
The formula explained
- Naegele’s rule
- due date = first day of last period + 280 days (adjusted for cycle length)
- Conception
- ≈ last period + 14 days
- IVF
- counted back from the transfer date and embryo age
Tips and common mistakes
- Only about 4 % of babies arrive on the exact due date.
- An early ultrasound date is more accurate than one from the last period.
- This is for information only — follow your midwife or doctor.
Questions people ask
How is the due date worked out?
From the first day of the last period, add 280 days (40 weeks) — Naegele’s rule. This assumes a 28-day cycle with ovulation around day 14; longer or shorter cycles shift the date.
When does each trimester start?
The first trimester runs to the end of week 13, the second covers weeks 14–27, and the third starts at week 28 and lasts until birth.
How is the date found after IVF?
From the transfer date: add 261 days for a day-5 (blastocyst) transfer, or 263 days for a day-3 transfer. The clinic’s own date takes priority.
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Enter your values to get the result with the formula, substituted values and an explanation of each step.