IVF due date calculator

How IVF due dates are worked out

Pregnancy is dated as 280 days — 40 weeks — from the last menstrual period, and by convention the LMP falls 14 days before ovulation. In an IVF cycle, egg retrieval stands in for ovulation, so the due date lands 266 days after retrieval.

An embryo transferred on day 5 was created five days before that transfer, so those five days come off the total. That's where the familiar numbers come from:

• Day 3 (cleavage-stage)transfer date + 263 days
• Day 5 (blastocyst)transfer date + 261 days
• Day 6 (blastocyst)transfer date + 260 days
• Egg retrievalretrieval date + 266 days

Why IVF dating is more precise

With natural conception, ovulation is estimated from the last period and can be several days out. With IVF, the date of fertilization is known exactly — which is why an IVF due date carries none of that guesswork. It's still an estimate of when labour starts, but the gestational age behind it is solid.

Frozen transfers

Time in storage doesn't count. A day-5 blastocyst transferred after two years frozen is dated exactly like a fresh day-5 transfer, because what matters is the embryo's age at transfer. Use the same setting above.

You're further along than you'd think

Because gestational age counts from a notional period two weeks before the embryo existed, you are already about two and a half weeks pregnant on transfer day — 2w 5d for a day-5 blastocyst. It catches almost everyone out, and it's why the first scan comes sooner than expected.