Calculate Your Due Date

Calculate from

First Day of Last Period

Conception Date

IVF Transfer Date

Average Cycle Length

Estimated Due Date

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How is a Due Date Calculated?

The standard method 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 and ovulation on day 14. For longer or shorter cycles, the calculator adjusts accordingly.

Calculation Methods

From LMP: Most accurate if your cycle is regular. LMP + 280 days = estimated due date.

From Conception: If you know when you conceived, add 266 days (38 weeks).

From IVF: For day-3 transfers, add 263 days. For day-5 blastocyst transfers, add 261 days.

What is a Trimester?

Pregnancy is divided into three trimesters. The first trimester (weeks 1–13) includes early development. The second (weeks 14–26) is often the most comfortable. The third trimester (weeks 27–40) brings rapid growth toward birth.

Only 4% of Babies are Born on Their Due Date

The due date is an estimate. Most babies are born between week 37 and 42. A birth between weeks 37 and 40 is considered full-term. The due date helps doctors monitor development, not predict the exact birth day.

FAQs

How accurate is a due date calculator?

The calculator gives an estimated due date based on Naegele's Rule. It's accurate to within 1–2 weeks for most pregnancies with regular cycles. Ultrasound measurements in the first trimester are the most accurate way to confirm your due date.

What if my cycle is not 28 days?

The calculator adjusts for cycle length. If your cycle is longer than 28 days, ovulation (and therefore conception) happens later, pushing the due date forward. Shorter cycles push it back.

When should I visit a doctor?

As soon as you have a positive pregnancy test. Your doctor or midwife will schedule your first prenatal appointment, typically around 8–12 weeks, and confirm your due date via ultrasound.

What is a full-term pregnancy?

A full-term pregnancy is between 39 and 40 weeks 6 days. Early-term is 37–38 weeks, late-term is 41 weeks, and post-term is 42+ weeks. Premature birth is before 37 weeks.

🤱 Due Date Calculator