See your actual odds of going into labor on any given day, based on NHS and CDC data
Try the Labor Probability Calculator
Enter your due date to see your personalized odds
Your due date is 40 weeks from your last period. But only 4-5% of babies arrive exactly on that day. Healthy pregnancies range from 37 to 42 weeks.
A probability calculator beats a single date. The real question isn't 'when will I go into labor?' but 'what are my chances this week?'
What the statistics show
4-5%
Born on due date
~50%
By due date
~80%
By 41 weeks
~100%
By 42 weeks
Several factors can shift your delivery date by a few days:
First pregnancy
— First-time mothers deliver 1-2 days later on average
Baby's sex
— Boys arrive about 1 day later than girls
BMI
— Higher BMI associated with later delivery (up to +5 days)
Twins/multiples
— Twins typically arrive 3 weeks early
Maternal age
— Age <25 or >40 may deliver slightly earlier
Most due date calculators give you one date. Ours shows conditional probability—your odds of going into labor given that you're still pregnant. At 41 weeks, for example, your daily odds are much higher than at 38 weeks because fewer pregnancies remain.
The model uses a Johnson SU distribution fitted to NHS Maternity Statistics 2023-24 and CDC Natality Data 2023, covering everything from extremely preterm to post-term deliveries.
Try the Labor Probability Calculator
Enter your due date to see your personalized odds