Overview
What this tool does
A pregnancy due-date calculator estimates when a baby will arrive. The standard medical method (Naegele's rule) counts 40 weeks from the first day of the last menstrual period (LMP). This calculator supports three input methods: LMP (with optional cycle-length adjustment), known conception date (+266 days), or IVF transfer date (with embryo-age adjustment for day-3 vs day-5 transfers). Beyond the due date itself, it tells you the current pregnancy week, trimester, estimated conception date, and a week-by-week milestone timeline so you can see what's coming next. Runs entirely in your browser; no signup.
How to
Use it in 3 steps
- Pick the method you have data for: LMP (most common), Known Conception (if tracking ovulation), or IVF Transfer (with the embryo age).
- Enter the date. For LMP, adjust cycle length if yours isn't 28 days.
- Read the due date and current pregnancy week.
- Scroll down to see the milestone timeline with calendar dates for each major week.
FAQ
Frequently asked questions
▶How accurate is this estimate?
Useful as a planning anchor, not as a precise prediction. Only about 5% of babies arrive exactly on the calculated due date. The 'normal' delivery window stretches from ~38 weeks to ~42 weeks; anything in there is considered full-term. Your healthcare provider may refine the estimate using a first-trimester ultrasound (crown-rump length measurement is accurate to within a few days).
▶Why does cycle length matter?
Naegele's rule assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, ovulation shifts and so does conception. We add (cycle_length - 28) days to the estimate. If you have very irregular cycles, the LMP method may be less reliable; consider the conception or IVF methods if you have that data.
▶What does 'embryo age at transfer' mean for IVF?
IVF embryos are cultured in the lab for either 3 days (cleavage stage) or 5-6 days (blastocyst) before transfer. The due-date math is the same starting point (266 days from conception) but the conception date is the embryo's age before transfer plus the transfer date. We do this adjustment automatically.
▶What's the trimester breakdown?
First trimester: weeks 1-12. Second trimester: weeks 13-26. Third trimester: weeks 27-40+. These are clinical conventions; some sources draw the lines slightly differently but the variation is small.
▶Is my data sent anywhere?
No. Date math runs in your browser. The dates you enter never leave your device.
▶Why does the timeline show calendar dates?
Knowing 'week 20' is abstract; seeing 'Tuesday, Aug 12' makes scheduling appointments, time off, and preparation much easier. Calendar dates derive from your due date by subtracting the appropriate number of weeks.
▶I'm past my due date and worried.
Up to about 42 weeks is still within the normal range. Past 40 weeks your provider will increase monitoring (non-stress tests, biophysical profile). Most providers consider induction at 41-42 weeks if labor hasn't started naturally. Talk to your doctor or midwife rather than relying on a web calculator.