Due Date Calculator
Estimate your expected delivery date from the first day of your last menstrual period.
Reviewed October 7, 2026 Runs in your browser — inputs are never stored
This tool provides general educational estimates only and is not medical advice. It does not diagnose, treat, or replace guidance from a qualified healthcare provider. Consult a doctor for decisions about your health.
About the Due Date Calculator
The due date calculator estimates when your baby is due from the first day of your last menstrual period, using Naegele’s rule: add 280 days (40 weeks). It also shows the dates on which the second trimester (week 14) and third trimester (week 28) begin, so you can plan appointments, leave and preparations. The rule assumes a regular 28-day cycle with ovulation on day 14, which is why only a small share of babies are born on the exact date and most arrive within two weeks either side. A dating ultrasound in the first trimester is more accurate and usually replaces the calendar estimate.
How to use it
- 1Enter the first day of your last period or known conception details as prompted.
- 2Set cycle length if your tool supports it.
- 3Review estimated due date and pregnancy week.
- 4Save or print the summary for your records.
- 5Verify with professional prenatal care.
Worked example
LMP 10 February → EDD near 17 November. Mid-August corresponds to about 26 weeks (second trimester). Use ultrasound dating when cycles are irregular — LMP-based estimates can shift by a week or more.
How it works
How it works
Naegele’s rule adds 280 days (40 weeks) to the first day of your last period.
Frequently asked questions
A:Most babies arrive within two weeks either side of the estimated date.
A:Add 266 days to the conception date instead, or consult your provider for a dating ultrasound.
Reviewed for accuracy · Last updated October 7, 2026
Formulas follow recognised clinical references — including WHO BMI classifications, the Mifflin-St Jeor equation, and Naegele’s rule — and are periodically checked against published reference values.
CalcWisee Editorial Team
Calculator development and formula review
CalcWisee is an independent site founded by Ayman. Every calculator is built from a published formula or official definition, tested against hand-worked examples before it goes live, and corrected promptly when a reader reports an issue to ayman@calcwisee.com.
Expertise: Financial mathematics, Health and fitness formulas, Applied mathematics, Unit conversion standards
References & sources
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