How the twin due date calculator works
A twin pregnancy is dated in exactly the same way as a single pregnancy: the estimated due date is 40 weeks (280 days) after the first day of your last period, 266 days after conception, or worked out from your IVF transfer. The calculator shows that date — but because twins are usually born earlier, it also shows the typical average birth for twins and the planned delivery window commonly recommended for your type of twins.
Types of twins and typical delivery timing
| Type | What it means | Commonly recommended delivery (uncomplicated) |
|---|---|---|
| Dichorionic-diamniotic | Each baby has its own placenta and sac (all non-identical and some identical twins) | 38+0 to 38+6 weeks |
| Monochorionic-diamniotic | Shared placenta, separate sacs (identical twins) | 34+0 to 37+6 weeks |
| Monochorionic-monoamniotic | Shared placenta and sac (rare) | 32+0 to 34+0 weeks |
Timings follow guidance from the American College of Obstetricians and Gynecologists (ACOG) for twin pregnancies without complications. Your own plan may differ.
Why twins arrive earlier
Carrying two babies stretches the uterus further and places more demands on the body, so labour often starts earlier, and some complications are more common. On average, twins are born around 35 weeks, and more than half are born before 37 weeks. Twin pregnancies therefore have more frequent check-ups and scans, often with a specialist team.
Preparing for an earlier arrival
- Plan as if your babies might come several weeks before the due date: pack your hospital bag and arrange help earlier.
- Learn the signs of preterm labour — regular tightening, fluid leaking, bleeding, pelvic pressure — and call straight away if you notice them.
- Ask your care team about the plan for birth, and whether a neonatal unit is available where you will deliver.
Weight gain and calorie needs are higher with twins: see the Pregnancy Weight Gain Calculator. For a single-baby due date, use the Due Date Calculator.