Chance of going into labor by week
Spontaneous labor odds from 37 to 42 weeks, with cumulative figures
Last updated
See the chance of labor by week as spontaneous labor rises from 37 weeks, peaks at 40 weeks, and becomes very high for anyone still pregnant at 41 weeks. About half of babies have arrived by the due date and about four in five by 41 weeks. The figures below are for singleton pregnancies, from NHS Maternity Statistics 2023-24 and CDC data, as fitted by the model on this site.
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Week-by-week labor probability
| Week | Labor starts this week | Born by end of week |
|---|---|---|
| 37 weeks | 3 to 5% | about 10% |
| 38 weeks | 8 to 10% | about 20% |
| 39 weeks | 15 to 18% | about 35% |
| 40 weeks | 20 to 25% | about 55% |
| 41 weeks | 25 to 35%* | about 80% |
| 42 weeks | very high* | about 100% |
What each week means
37 weeks: early term
Lungs are usually mature. Labour now is common and generally safe, though some babies need extra monitoring.
38 weeks: full term begins
The baby is ready for birth. Braxton Hicks contractions often get stronger around now.
39 weeks: peak readiness
Spontaneous labour becomes more common. The ARRIVE trial found benefits from induction at 39 weeks for some first-time mothers.
40 weeks: the due date week
Statistically the most likely week for spontaneous labour. About half of pregnancies have delivered by the end of it.
41 weeks: late term
If you have not delivered, your daily odds are high. Most providers discuss induction this week.
42 weeks: post-term
Nearly all remaining pregnancies deliver this week, spontaneously or by induction. NICE recommends offering induction between 41+0 and 42+0.
First baby or later baby
First pregnancies deliver 1 to 2 days later on average than later pregnancies. The shift is small compared with the width of the curve, so it changes which day is most likely rather than which week. The calculator applies it automatically.
What changes after 41 weeks
Spontaneous labour becomes less common after 41 weeks because most pregnancies that reach that point are induced. NICE recommends offering induction between 41+0 and 42+0 weeks; US guidance from ACOG advises discussing induction at 41 weeks. The model is truncated at 42 weeks for this reason.
Prepare for birth
Three picks the evidence supports, with its limits
Practical items for the last weeks. The studies looked at the food or the technique, not these brands. As an Amazon Associate I earn from qualifying purchases.
Evidence: Date Fruit and Labor · Birthing Ball and Labor Outcomes · Perineal Massage and Tearing
Evidence is limited and cannot predict your birth. None of these starts labour on a schedule. Ask your clinician what is appropriate for you.
Read the 2026 research updateSee your own odds, day by day
Enter your due date for probabilities fitted to NHS and CDC birth data.
Frequently asked questions
What are the chances of going into labour at 37 weeks?
At 37 weeks about 3 to 5% of pregnancies go into spontaneous labour during that week. About 10% of all babies are born before 37 weeks. A baby born now is early term and the lungs are usually mature.
What are the chances of going into labour at 38 weeks?
About 8 to 10% of pregnancies go into labour during week 38, and about 15 to 20% of babies have been born by the end of it. From 38 weeks the baby is considered full term.
What are the chances of going into labour at 39 weeks?
About 15 to 18% of pregnancies start labour in week 39, and about 25 to 30% of babies have been born by the end of it.
What are the chances of going into labour at 40 weeks?
Week 40 is the most likely week, with about 20 to 25% of pregnancies starting labour. About 50 to 55% of babies have been born by the end of the due date week.
What are the chances of going into labour at 41 weeks?
If you reach 41 weeks still pregnant, your odds that week are high: roughly 25 to 35% in conditional terms. About 80% of all babies have arrived by 41 weeks, and most care providers discuss induction at this stage.
Do these numbers include inductions?
No. They describe spontaneous labour. Induced and planned births follow a schedule and are not part of the curve.