A twin pregnancy calculator with the typical birth week
Twins are rarely born on their due date. This twin pregnancy calculator gives you both dates that matter: the standard 40-week due date, worked out from your last period, your IVF transfer or the date from your scan, and the week in which birth is usually planned for your type of twins — which depends on whether the babies share a placenta or a sac — following the UK’s NICE guideline on twin and triplet pregnancy.
It also shows how many weeks pregnant you are today and when each trimester starts. It is information only, not medical advice: twin pregnancies are closely monitored, and your obstetric team will plan the birth with you.
How to use the Twin Pregnancy Due Date Calculator
- Choose what you know: your last period, your IVF transfer date, or the due date from your scan.
- Enter the date (and cycle length or embryo age if asked).
- Choose the type of twin pregnancy your early scan showed.
- Read the typical planned-birth window, the due date and the key dates, then copy them to share with your partner or keep in your notes.
Twin Pregnancy Due Date Calculator features
Due date three ways
Last period with cycle length, IVF day-3 or day-5 transfer, or a scan date.
Birth timing by type
DCDA, MCDA, MCMA twins and triplets, from NICE NG137.
Today’s week
How many weeks and days pregnant you are, and how long until the window.
Clearly sourced
Each timing names the NICE recommendation it comes from.
When are twins usually born?
| Type (uncomplicated pregnancy) | Planned birth offered (NICE NG137) |
|---|---|
| Dichorionic diamniotic twins — each baby has its own placenta | At 37 weeks |
| Monochorionic diamniotic twins — shared placenta, separate sacs | At 36 weeks, after considering steroids |
| Monochorionic monoamniotic twins — shared placenta and sac | Between 32+0 and 33+6 weeks |
| Triplets — trichorionic or dichorionic triamniotic | At 35 weeks |
Why twins arrive early
NICE says about 60 in 100 twin pregnancies end with a spontaneous birth before 37 weeks, and about 75 in 100 triplet pregnancies before 35 weeks. For uncomplicated pregnancies, planned birth at the times above is offered because continuing longer increases the risk of stillbirth, while birth at those weeks has not been linked with more serious problems for the babies. Complications such as twin-to-twin transfusion syndrome or growth differences change the plan.
In the United States, the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine publish their own timing recommendations for twins; ask your obstetrician which applies to you. For the standard due-date methods and scan dating, see the pregnancy due date calculator; to count down the days, the pregnancy countdown.
Twin Pregnancy Due Date Calculator FAQ
How do you calculate a twin due date?
The same way as for one baby: 280 days after the first day of your last period, adjusted for cycle length, or from the IVF transfer date. Twins are then usually born earlier than that date.
How many weeks are twins born?
Many twins are born before 37 weeks. In uncomplicated pregnancies, NICE advises offering planned birth at 37 weeks for twins with separate placentas and 36 weeks for twins sharing a placenta.
How do I calculate an IVF twin due date?
Add 261 days to a day-5 transfer date or 263 days to a day-3 transfer date. Choose “My IVF embryo transfer date” above.
Can twins be born at 40 weeks?
Some are, but NICE advises offering planned birth earlier for uncomplicated twins, because continuing beyond 37+6 weeks (36+6 weeks if the babies share a placenta) increases the risk of stillbirth.
Is the twin due date the same as for one baby?
Yes, the 40-week due date is calculated the same way. What differs is when birth is usually planned, which this page shows for your type of twins.
Can I see my twin pregnancy week by week?
The page shows how many weeks and days pregnant you are today and the dates of the trimesters. For typical sizes week by week, see the baby size by week chart; twins are often a little smaller in late pregnancy, and your scans track their growth.
What does dichorionic mean?
Each baby has its own placenta (chorion). Monochorionic twins share a placenta; monoamniotic twins also share the amniotic sac. Your early scan shows which type you have.