Same due date, earlier birth
Multiples are dated exactly like singletons, so your official due date is still 40 weeks from the last period. What differs is delivery: twins average about 36 to 37 weeks and triplets 32 to 34, partly because labour starts earlier and partly because planned birth is offered before the risks of continuing outweigh the benefits.
The windows on this page follow NICE guidance on twin and triplet pregnancy: planned birth from 37 weeks for dichorionic twins, 36 for monochorionic, and about 35 for triplets, when the pregnancy is otherwise uncomplicated.
Related tools
For the weekly count, use the how far along am I page. After IVF, the IVF due date calculator gives the singleton date with embryo-age detail. Curious how likely twins were in the first place? The chance of twins calculator explains the factors.
Frequently asked questions
How is a twin due date calculated?
Exactly like a singleton: 40 weeks from the last period, or 38 weeks from conception or transfer. That 40-week date stays on your notes for dating scans and appointments. What changes is when the babies are likely to arrive: the average twin pregnancy lasts about 36 to 37 weeks, so the calculator shows that window as well.
When are twins usually born?
The average is around 36 to 37 weeks and about 60% of twins arrive before 37 weeks. For uncomplicated twins with separate placentas (dichorionic), NICE recommends offering planned birth from 37 weeks; for twins sharing a placenta (monochorionic), from 36 weeks, because the risks of continuing rise after that.
When are triplets usually born?
Around 32 to 34 weeks on average, with planned birth usually offered at about 35 weeks if the pregnancy has been straightforward. Almost all triplets are born before 37 weeks and most need some time in neonatal care.
Is a twin pregnancy dated differently after IVF?
No. A day-5 transfer is dated as 2 weeks 5 days on transfer day, the same as any IVF pregnancy, and the 40-week date follows from that. The calculator's IVF mode handles it. Double embryo transfers carry roughly a 25% chance of twins, which is why single transfers are now standard for most people.
Why does my clinic keep the 40-week date if twins come early?
Because gestational age, not the expected birth day, is what every scan, blood test and growth chart is measured against. Your care team will talk about a planned birth week separately, usually from around 28 weeks onward once they know how the pregnancy is going.
These calculators give estimates based on cycle averages and standard formulas. They are for general information only and are not medical advice. For anything concerning your health or pregnancy, talk to a qualified healthcare provider.