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Is Baby Coming?

Labour & labor probability calculator · NHS and CDC data

No one knows when.
We know how likely.

Only about 4% of babies arrive on their due date. Enter yours and see the chance that labour starts on each day and in each week, fitted to NHS and CDC birth data and adjusted for your pregnancy.

Estimated due date

Free, no account neededSpontaneous labour only, not inductionsNHS 2023-24 and CDC 2023 data

Fig. 01

A representative labour distribution

Daily chance of spontaneous labour · NHS/CDC-fitted model

  1. Step 1

    Enter your due date

    Today is placed on a probability curve fitted to NHS and CDC birth statistics, so the odds reflect that you are still pregnant.

  2. Step 2

    Add what shifts the curve

    A first pregnancy, BMI, age, the baby's sex and twins move the expected date by days, not weeks. Each factor cites its study.

  3. Step 3

    Plan around the odds

    See the chance labour starts before a wedding or a flight, and which window (early, on time, late) is most likely for you.

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.

Natural Delights Pitted Dates, 12 ozA small, ready-to-eat pack, so you can try dates without buying in bulk.Evidence for dates in late pregnancy is promising but limited. Date size varies and no ideal amount is established. If you have diabetes, check your care plan first.View On AmazonTrideer Pregnancy BallAnti-burst ball with a pump and guide. Evidence that a ball lowers labour pain is moderate-to-low certainty.Choose the size by seated fit: feet flat on the floor, hips just above the knees. Follow the maker's sizing and inflation instructions and keep something to hold for balance.View On AmazonLansinoh Massage Oil, 1.7 fl ozPerineal massage from about 34 to 36 weeks was linked to fewer episiotomies in first births.Contains sweet almond and wheatgerm oils, so check for ingredient allergies. The massage technique is what the evidence covers, not the brand.View On Amazon

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 update

Labour & labor probability calculator: what the odds tell you

This labour probability calculator—called a labor probability calculator in US English—turns a due date into odds. Instead of one date, it shows the chance that spontaneous labour starts on each day and the cumulative chance by each week, given that you are still pregnant today. This calculator uses a distribution fitted to NHS Maternity Statistics 2023-24 and CDC natality data for 2023, and adjusts the curve for the personal factors that research shows shift timing.

The figures are for spontaneous labour. Roughly half of births in England and a third in the United States now start with an induction or a planned caesarean, so if a birth is scheduled your timing will follow that plan. The methodology page explains the model, its calibration and its limits.

Labour by week, from the model

Model values for a singleton pregnancy with no personal adjustments. The second column is the share of all births that start in that week; the third is the share born by the end of it.

Spontaneous labour only. Values from the NHS/CDC-fitted model; see the methodology page for calibration targets.
Gestational weekLabour starts this weekBorn by end of week
37 weeks5%15%
38 weeks12%27%
39 weeks22%49%
40 weeks27%76%
41 weeks22%98%
42 weeks2%100%

For the week-by-week detail and what changes after 41 weeks, read chance of labor by week. If you are wondering what the body does before labour, see signs labour is coming.

Frequently asked questions

When will I go into labour?

No one can predict the day. In NHS and CDC birth data about half of babies have arrived by the due date and about four in five by 41 weeks. The calculator turns your due date into odds for each day and week from today.

What are my chances of going into labour today?

It depends on how far along you are. With no personal adjustments, the model puts the chance of labour starting on a given day at about 3% at 39 weeks, 8% at 40 weeks and 15% at 41 weeks, because each day that passes without labour raises the odds for the next.

How accurate is a labour probability calculator?

It is a population estimate, not a prediction for you. The model is fitted to official birth statistics, and studies show that individual timing is hard to predict (a c-statistic of about 0.56). Use the odds for planning, not for medical decisions.

Does the calculator include inductions and planned caesareans?

No. The odds are for spontaneous labour only. If an induction or a planned birth is scheduled, your delivery timing will follow that plan instead.

Does a second or third baby change the odds?

Yes. First pregnancies run slightly later on average and later pregnancies slightly earlier, so the calculator adjusts for parity. BMI, maternal age, the baby's sex and twins or triplets shift the curve too.

How does this labor likelihood calculator work?

A Johnson SU distribution fitted to NHS and CDC birth timing, truncated at 42 weeks. Conditional probability is applied so the numbers reflect that you are still pregnant today.

What are the signs that labour is coming?

Common early signs are the baby dropping lower, stronger Braxton Hicks contractions, losing the mucus plug, loose stools and a burst of energy. Active labour means regular contractions that get stronger and closer together. Call your midwife or maternity unit if your waters break or you have bleeding.