Pregnancy Due Date Calculator

Pregnancy Due Date Calculator

Calculate estimated due date from last period, conception, or IVF date. Week-by-week milestones.

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Default: 28 days (21-35 range)

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How the Due Date Is Calculated

This calculator uses Naegele's Rule, the standard medical formula for estimating the Expected Date of Delivery (EDD). It takes the first day of your Last Menstrual Period (LMP), adds one year, subtracts three months, and adds seven days. This assumes a 28-day menstrual cycle with ovulation on day 14, resulting in a 280-day (40-week) estimated pregnancy.

If you know the conception date, the calculator adds 266 days (38 weeks) from that date instead.

Pregnancy Trimesters

  • First trimester - Weeks 1 to 12. Major organ development begins. This is when most early pregnancy symptoms occur.
  • Second trimester - Weeks 13 to 26. Often considered the most comfortable period. Fetal movement becomes noticeable.
  • Third trimester - Weeks 27 to 40. Rapid growth and preparation for delivery. Full-term is considered 37 to 42 weeks.

How Accurate Is the Estimated Due Date?

Only about 4-5% of babies are born on the exact calculated due date. Most deliveries occur within two weeks before or after the EDD. The estimate is less accurate for women with irregular cycles or cycles that differ significantly from 28 days. A first-trimester ultrasound provides a more personalised estimate.

This calculator provides an estimate only and is not a substitute for professional medical advice. Consult your healthcare provider for personalised guidance, ultrasound-based dating, and prenatal care.

Frequently Asked Questions

How is the pregnancy due date calculated?+
This calculator uses Naegele's Rule: add 280 days (40 weeks) to the first day of your Last Menstrual Period (LMP). This assumes a 28-day cycle with ovulation on day 14. If you know the conception date, it adds 266 days (38 weeks) instead.
How accurate is the estimated due date?+
Only about 4-5% of babies are born on the exact calculated due date. Most deliveries occur within two weeks before or after the EDD. The estimate is less accurate for women with irregular cycles. A first-trimester ultrasound provides a more personalised estimate.
What are the three pregnancy trimesters?+
First trimester: weeks 1-12 (major organ development). Second trimester: weeks 13-26 (fetal movement begins). Third trimester: weeks 27-40 (rapid growth, preparation for delivery). Full-term is considered 37-42 weeks.
Can I calculate based on conception date or IVF transfer?+
Yes. If you know the conception date, the tool adds 266 days (38 weeks). For IVF, the calculation depends on whether a Day 3 or Day 5 embryo was transferred - the tool accounts for this.
Is this a substitute for medical advice?+
No. This calculator provides an estimate only. Consult your healthcare provider for personalised guidance, ultrasound-based dating, and prenatal care.