User Rating 0.0 ★★★★★

Total Usage 2 times

Category Womens Health

First Day of Last Period (LMP)

Your Estimated 40-Week Date:
-
Target Twin Date (37 Weeks):
-

Twin Timeline

First Trimester Ends: -
Second Trimester Ends: -
34 Weeks (Lung Maturity): -

Is this tool helpful?

Your feedback helps us improve.

★ ★ ★ ★ ★

About

Discovering you are expecting twins is an exciting milestone that changes your pregnancy timeline. While a standard singleton pregnancy is calculated at 40 weeks (280 days), the average gestation for twins is shorter. Most medical professionals consider 37 weeks (259 days) to be 'term' for twins to minimize risks such as placental insufficiency.

This calculator modifies the standard Naegele’s Rule to provide a more realistic Estimated Due Date (EDD) for multiples. It also breaks down your pregnancy into trimesters, helping you plan for the earlier arrival of your babies.

Formulas

Standard Naegele's Rule adds 280 days to the LMP. For twins, we adjust the target.

EDD_twins = LMP + 259 days (37 weeks)

Reference Data

Milestone	Singleton (40w)	Twins (37w Target)	Notes
First Trimester Ends	Week 13	Week 13	Organogenesis complete.
Viability	Week 24	Week 24	Survival possible with NICU care.
Third Trimester	Week 28	Week 27	Rapid growth phase begins.
Preterm Labor Risk	Low	High	Monitoring increases after Week 30.
Early Term	37 Weeks	34-36 Weeks	Lungs often mature by week 34-35.
Full Term	40 Weeks	37-38 Weeks	Common induction window for twins.

Frequently Asked Questions

The uterus has a limit to how much it can stretch. With two babies, two placentas, and double the amniotic fluid, this limit is reached sooner. Additionally, risks of complications like preeclampsia increase after 37-38 weeks.

No. While 37 weeks is 'early term' for a singleton, it is widely considered full term for twins. Many doctors will recommend induction by week 38 if labor hasn't started naturally.

This calculator uses the general average (37 weeks). However, MoDi (Monochorionic-Diamniotic) twins sharing a placenta are often delivered earlier (36 weeks) to prevent complications, while MoMo twins are delivered even earlier (32-34 weeks). Consult your OBGYN.