Wondering when your twins or triplets are due? Enter your details to get an instant 40-week EDD and the typical delivery window for multiples (based on the dating method you choose). Curious about odds? See the chance of twins for your age and history.

Updated Jul 2026

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Methodology & sources

EDD dating: 280 days (40 weeks) from LMP (Naegele’s rule); or by early ultrasound (EDD = scan date + (280 days − measured GA)); or for IVF/FET by adding ~263 days (day-3), 261 days (day-5), or 260 days (day-6) to the transfer date.

Multiples timing (uncomplicated): di/di ≈ ~38w; mono/di ≈ ~36–37w; mono/mono ≈ ~32–34w; triplets ≈ ~35–36w. Final timing is individualized by your care team.

See How it works and Data sources for citations.

For a simple singleton due date from your last period or ultrasound, use the Pregnancy Due Date Calculator.

Frequently asked questions

How accurate is the twins/triplets due date?

EDD is a 40-week baseline. Multiples often deliver earlier; timing is individualized by your care team.

What if I conceived via IVF/FET?

EDD can be calculated from transfer date and embryo day (3/5/6). Your clinic may confirm/adjust with early ultrasound.

What is chorionicity and why does it matter?

It describes how twins share a placenta and sacs (di/di, mono/di, mono/mono). It guides typical delivery windows.

Should I use LMP or ultrasound to date the pregnancy?

Use your most reliable method. Early ultrasound commonly replaces LMP if they differ meaningfully.

Twin & Triplet Due Date Calculator