Pregnancy Due Date Calculator: When Will You Meet Your Baby?
A few details from you, and we'll map out your due date, current week, and what's happening with your baby right now — from the team that knows infant sleep best.
How does this work?
Three ways to start:
- First day of your last period — the most common method.
- Conception date — often the date of ovulation.
- Known due date — from your provider or an ultrasound.
Uses Naegele's rule: 280 days (40 weeks) from your last period, adjusted for cycle length.
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Your pregnancy at a glance
Your little —
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Calculate your due date to see your weekly milestone.
Sources: Cleveland Clinic · Mayo Clinic · NHS Inform · WebMD
How due dates actually work
A short read on the math behind your number
The 280-day rule
A standard pregnancy is calculated as 280 days — or 40 weeks — from the first day of your last menstrual period. That's because pregnancy is dated from before conception actually happens. By the time most people get a positive test, they're already considered four weeks along.
If you know your conception date, the math runs from there instead: 266 days, or 38 weeks. Same finish line, different start line.
Why your due date is an estimate
Only about 5% of babies arrive on their actual due date. The vast majority show up sometime between 37 and 42 weeks — what doctors call "term." Your provider may adjust your due date after your first ultrasound, especially if your cycle is irregular.
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FAQs
How accurate is a due date calculator?
Due date calculators give a reliable estimate, but they're not exact. Only about 5% of babies arrive on their precise due date — most arrive within a two-week window before or after, which is completely normal. An early ultrasound is the most accurate way to confirm or adjust your due date.
What if I have an irregular cycle?
If your cycle is longer or shorter than 28 days, choose your average cycle length in the calculator. For very irregular cycles, the calculator may be less precise — your provider will use an early ultrasound to give you the most accurate dating.
How likely am I to give birth on my due date?
About 1 in 20 babies arrive on their estimated due date. The vast majority arrive between 37 and 42 weeks — what providers call "term." Arriving a little early or a little late is completely normal.
Can my due date change?
Yes. Your provider may adjust your due date after your first ultrasound, especially if your cycle is irregular or if early measurements suggest a different timeline. The updated date is usually the one your care team uses thereafter.
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