Due Date Calculator
Find your estimated due date in seconds. Calculate from the first day of your last period (with your own cycle length) or from a known conception date.
Estimates only. Just 1 in 20 babies arrive on their exact due date — your provider’s dating scan is the most accurate guide.
How it works
Pregnancy is dated from the first day of your last menstrual period (LMP), not from conception. A full-term pregnancy lasts about 40 weeks from your LMP. If you know the date you conceived instead, switch to the conception tab and we’ll count forward 38 weeks.
Because ovulation timing depends on your cycle length, adjusting the slider gives you a more personalized estimate than a one-size-fits-all calculator.
How this is calculated
From your last period we use Naegele’s rule: 280 days (40 weeks) from the first day of your last period, adjusted for your cycle length. From a conception or ovulation date we add 266 days.
A due date is an estimate, not a deadline — only about 1 in 20 babies arrive exactly on it, and a full-term birth is anywhere from 37 to 42 weeks.
Sources: ACOG, Mayo Clinic
Last reviewed: 2026-06
Frequently asked questions
How is my due date calculated? +
The most common method (Naegele’s rule) adds 280 days — 40 weeks — to the first day of your last menstrual period, assuming a 28-day cycle. We adjust this estimate for your actual cycle length. From a known conception date, we add 266 days (38 weeks).
How accurate is a due date calculator? +
It gives a reliable estimate, but only about 1 in 20 babies arrive on their exact due date. A normal full-term birth happens anytime between 37 and 42 weeks. An early dating ultrasound is the most accurate guide.
What if I have an irregular cycle? +
If your cycle is irregular, the last-period method is less reliable. Use the conception-date option if you tracked ovulation, and confirm with your provider’s dating scan.
Related reading
- Mucus Plug and Bloody Show: What Do They Mean?Losing your mucus plug or seeing bloody show is a normal late-pregnancy sign, but it does not always mean labour is starting right now. Here is what to know and when to call.Jun 17, 2026 · 4 min readRead more→
- When Is a Baby Considered Full Term?Full term is 39 0/7–40 6/7 weeks, but babies born 37–42 weeks are generally considered term. Here are the term categories and what they mean for your due date.Jun 2, 2026 · 3 min readRead more→
- How Accurate Is Your Due Date?Only about 1 in 20 babies arrive on their due date. Here’s how accurate due dates really are, why babies come “late,” and what the 37–42 week window means.May 30, 2026 · 5 min readRead more→
- How to Calculate Your Due Date (3 Simple Methods)Learn how your estimated due date is worked out from your last period, conception date, or ultrasound — and why babies rarely arrive on the exact day.May 30, 2026 · 5 min readRead more→
More tools for this stage
Conception Date Calculator
Work backwards from your due date or last period to estimate when conception happened.
Weeks to Months Converter
Turn pregnancy weeks into months, weeks left, and your trimester.
Pregnancy Calendar
Turn your due date into a calendar of scans, milestones and the big day — add it to Apple, Google or Outlook.
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