How is the due date calculated?

Naegele's rule: first day of last menstrual period + 280 days (40 weeks). The calculator also offers the conception date method (+ 266 days) for known conception dates.

How accurate is the estimated due date?

Only about 4% of babies arrive on the exact predicted date. 80% arrive within ±2 weeks of it. Ultrasound dating in the first trimester is more accurate than LMP.

What if my cycle isn't 28 days?

Cycles longer or shorter than 28 days shift the conception window. The calculator adjusts for cycle length so the due date estimate stays accurate.

🤰 Pregnancy Due Date Calculator

Estimate your baby's due date, current week of pregnancy, and trimester. Based on Naegele's Rule — the globally accepted clinical standard. All calculations run in your browser — no data is stored or shared.

First Day of Last Menstrual Period (LMP)

Average Cycle Length (days)

⚠️ Not medical advice. This calculator provides an estimate only. Due dates can vary. Consult your midwife or obstetrician for a confirmed estimated delivery date (EDD) based on ultrasound measurements.

About This Calculator

The Pregnancy Due Date Calculator uses Naegele's Rule — the standard clinical method for estimating a baby's due date. The formula adds 280 days (40 weeks) to the first day of your last menstrual period (LMP), adjusted for cycle lengths other than 28 days.

How Naegele's Rule Works

Naegele's Rule is based on an average human gestation of 280 days (40 weeks) from the LMP. If your cycle is longer or shorter than 28 days, the estimated due date is adjusted accordingly:

EDD = LMP + 280 days + (Cycle Length − 28) days

Understanding Trimesters

First Trimester (Weeks 1–13): Major organ development begins. Risk of miscarriage is highest in early weeks.
Second Trimester (Weeks 14–26): Baby grows rapidly. Many parents find out the sex during this period.
Third Trimester (Weeks 27–40): Final development and preparation for birth.

Important Notes

Only about 5% of babies are born exactly on their due date. A baby is considered full-term from 39 weeks. Your midwife or doctor will typically confirm your EDD using an early ultrasound scan (dating scan), which is more accurate than LMP-based calculations.

⚠️

Important Note: This tool is intended to provide estimates and should not be used as a substitute for professional advice. Information generated by these calculators may be incomplete and does not account for all individual circumstances. Always seek the counsel of a certified expert (such as a financial advisor, healthcare provider, or licensed engineer) before taking action based on these results.

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