What Is a Due Date Calculator?
This calculator estimates a pregnancy due date using several common methods — last menstrual period (LMP), a known conception date, or an IVF embryo transfer date — since the calculation differs depending on which reference point you know.
How to Use the Due Date Calculator
- Select the method that matches what you know.
- Enter the relevant date.
- View your estimated due date and gestational age.
Due Date Formulas by Method
Worked Example
Due date: January 15 + 266 days ≈ October 8
Understanding Your Results
Each method accounts for the different starting reference point: LMP-based dating assumes ovulation around day 14 of a 28-day cycle, while conception-based and IVF-based dating start counting from a known biological event, which is often more precise when available.
Which Method Is Most Accurate?
IVF transfer dates are typically the most precise since the exact age of the embryo is known. A known conception date (e.g., from ovulation tracking) is also quite precise. LMP-based dating is the most common method but assumes a "typical" cycle and can be less accurate for those with irregular cycles — an early ultrasound often provides the most reliable estimate regardless of method.
Frequently Asked Questions
IVF transfer dates and known conception dates tend to be most precise since they're based on a specific known event. LMP-based dating is more commonly used but assumes a typical cycle, and an early ultrasound is often considered the most reliable overall.
Because conception occurs roughly 14 days after the start of the last period in a typical cycle, so counting from conception directly is about 14 days shorter than counting from LMP.
A 5-day blastocyst transfer places a more developed embryo, so fewer days remain until the standard 40-week (280-day) mark from conception, compared to a 3-day transfer.
They provide a statistically reasonable estimate, but only a small percentage of babies are born exactly on their calculated due date — most arrive within about two weeks of the estimate.
Yes — a healthcare provider can confirm dating with an early ultrasound, which is generally considered the most accurate method, especially for irregular cycles.