Our free due date calculator helps expectant parents determine their estimated due date using three different methods — last menstrual period (LMP), IVF embryo transfer date (3-day or 5-day blastocyst), or ultrasound gestational age. Each method is used by healthcare providers to calculate a due date as accurately as possible.

In addition to your due date, this calculator provides your current gestational age, the dates for each trimester, the date of fetal viability (24 weeks), and an estimated conception date. All calculations are based on standard obstetric formulas used by hospitals and clinics across the USA and Canada.

How to Use the Due Date Calculator

Choose your calculation method and follow the corresponding steps:

1. Last Menstrual Period (LMP): Enter the first day of your last period and your average cycle length.
2. IVF Transfer (3-day embryo): Enter the date of embryo transfer. The calculator adds 17 days to determine LMP equivalent.
3. IVF Transfer (5-day blastocyst): Enter the transfer date. The calculator adds 19 days to determine LMP equivalent.
4. Ultrasound: Enter the ultrasound date and the gestational age confirmed by ultrasound.
5. Click Calculate Due Date to see all pregnancy milestone dates.

When Should You Use a Due Date Calculator?

Use the due date calculator as soon as you confirm your pregnancy to establish a preliminary timeline. In particular, the LMP method is typically used as the starting point, with the due date refined by an early ultrasound (ideally between 8–12 weeks) which is the most accurate method for dating a pregnancy.

Furthermore, the due date calculator is especially helpful for IVF pregnancies, where the exact conception date is known and standard LMP calculation does not apply. Additionally, knowing key dates such as the viability threshold (24 weeks) and the start of each trimester helps you and your healthcare provider plan appropriate monitoring and care.

What to Expect at Each Stage of Pregnancy

Here is a brief overview of key milestones to prepare for:

• Weeks 1–13 (First Trimester): Morning sickness, fatigue, and early prenatal appointments. First trimester screening and NIPT testing if desired.
• Weeks 14–26 (Second Trimester): Often called the golden trimester. Anatomy scan at 18–20 weeks. Baby movements typically felt from weeks 16–22.
• Week 24 (Viability): The threshold at which survival outside the womb becomes possible with medical intervention.
• Weeks 27–40 (Third Trimester): Rapid fetal growth, GBS testing, weekly appointments near the end, and birth preparation.

Frequently Asked Questions About the Due Date Calculator

Is the LMP or ultrasound due date more accurate?

An early ultrasound (before 14 weeks) is generally considered more accurate for dating a pregnancy than the LMP method, particularly for women with irregular cycles. However, the LMP date is still widely used as the starting point.

What is gestational age vs fetal age?

Gestational age is counted from the first day of the last menstrual period and is what doctors use. Fetal age is counted from conception, which is approximately 2 weeks less than gestational age.

Related Calculators

Furthermore, you might find these related tools useful: Pregnancy Calculator — Pregnancy Conception Calculator

Disclaimer: Due dates are estimates only. Only about 5% of babies are born on their exact due date. Always follow your healthcare provider’s guidance for prenatal care and monitoring.