Pregnancy Due Date Calculator
Calculate your estimated due date and track pregnancy milestones
How It Works
Overview
A pregnancy due date calculator estimates when your baby is most likely to be born using the date of your last menstrual period (LMP). It uses Naegele's rule, the same formula doctors and midwives have used since 1812: due date = LMP + 280 days (40 weeks). This calculator also tells you your current gestational age (weeks and days), your current trimester, and key upcoming milestones.
A few caveats up front. The number is an estimate, not an appointment. Only about 5% of babies are born on their due date; most arrive within a two-week window before or after. Early-pregnancy ultrasounds, taken between weeks 8 and 13, are typically more accurate than LMP-based dating, especially if your cycles aren't a textbook 28 days. Use this tool for planning, but rely on your doctor for clinical decisions.
The Formula
Naegele's rule assumes a 28-day cycle with ovulation on day 14, so conception is roughly 2 weeks after LMP. The 40-week count therefore includes ~2 weeks before conception — actual gestation from conception is about 38 weeks.
Trimesters: 1st is weeks 1–13, 2nd is 14–27, 3rd is 28–birth. Full-term begins at 37 weeks. Most providers consider induction by 41–42 weeks if labor hasn't started spontaneously.
Worked Example
If your LMP was January 15, 2026:
- Add 280 days → estimated due date: October 22, 2026
- If today is May 1, 2026, that's 106 days after LMP = 15 weeks 1 day
- You're in the 2nd trimester
- Next milestone: 18 weeks (gender reveal possible) on May 22, 2026
For irregular cycles, an ultrasound dating performed before week 13 can shift this by ±1 week or more. Always defer to your provider's estimate.
When to Use This
- Early pregnancy — getting a rough timeline as soon as you confirm.
- Planning prenatal care — most providers schedule visits at specific gestational ages.
- Maternity leave — figuring out when to start, and how to coordinate with your employer.
- Tracking milestones — when to expect your first ultrasound, anatomy scan, glucose test, etc.
- Birthing class scheduling — most are taken in the third trimester.
Common Mistakes to Avoid
- Using conception date as LMP. LMP is the first day of your last period, about 2 weeks before conception.
- Trusting LMP with irregular cycles. If cycles vary by more than a few days, get an early ultrasound for accurate dating.
- Stressing about "going past" the due date. Anything between 37 and 42 weeks is normal full-term.
- Mixing up due-date estimates. Different methods (LMP, conception, ultrasound, IVF transfer) can give dates a week apart. Track which one you're using.
- Self-diagnosing complications. Tools like this don't replace prenatal care. See a provider regularly.
Frequently Asked Questions
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