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Pregnancy Due Date Calculator

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Guide

Pregnancy Due Date Calculator

Estimate your baby’s due date instantly from your last menstrual period, conception date, or IVF transfer date. Get your current gestational age, trimester, progress toward 40 weeks, and a complete timeline of key prenatal milestones and appointment windows — all calculated in your browser with no data sent to a server.

How to Use

Choose a calculation method – Last Menstrual Period (LMP), conception date, or IVF transfer date.
Enter the relevant date – the form adapts to your selection and only shows inputs you need.
Adjust your cycle length if needed – the default 28-day cycle suits most people; longer or shorter cycles shift the due date accordingly.
For IVF, select embryo age at transfer – Day 3 or Day 5 blastocyst.
Review your timeline – the estimated due date, current week and day, trimester, progress bar, and milestone windows update automatically.

Features

Three input methods – LMP (Naegele’s rule), conception date, or IVF transfer date with Day 3 / Day 5 support.
Cycle length adjustment – accurate results for 20–45 day cycles, not just the textbook 28-day default.
Estimated due date (EDD) – calculated with the standard 280-day formula adjusted for your method.
Current gestational age – exact weeks and days plus a total day count.
Trimester indicator – instantly know whether you’re in the 1st, 2nd, or 3rd trimester.
Visual progress bar – see how far along you are toward 40 weeks at a glance.
Appointment timeline – NT scan, anatomy scan, glucose screening, Tdap vaccine, and Group B Strep test windows.
Past-milestone markers – completed windows are checked off so you always know what’s next.
Live updates – every field change recalculates the entire timeline instantly.
Private & offline – all math runs in your browser; no dates are uploaded or stored.

 FAQ

What is Naegele's rule for calculating a due date?

Naegele's rule estimates the due date by adding 280 days (40 weeks) to the first day of the last menstrual period, assuming a regular 28-day cycle with ovulation around day 14. The original rule subtracts 3 months from the LMP and adds 7 days plus 1 year, which produces the same result. The method is named after German obstetrician Franz Karl Naegele and remains the standard reference in obstetrics today.
Why does cycle length affect the due date?

A pregnancy is conceived roughly two weeks before the next expected period, regardless of cycle length. People with longer cycles ovulate later than day 14, so their actual conception date is later than the textbook estimate. The 280-day rule assumes a 28-day cycle, so a 32-day cycle shifts the due date about 4 days later, while a 25-day cycle shifts it about 3 days earlier. Adjusting for cycle length produces a more accurate EDD.
How is gestational age different from fetal age?

Gestational age is measured from the first day of the last menstrual period, while fetal (or embryonic) age is measured from the date of conception. Because conception happens roughly two weeks after the LMP, gestational age is typically about 14 days greater than fetal age. Most clinicians, ultrasound reports, and pregnancy apps use gestational age, which is why a pregnancy is described as 40 weeks even though the embryo only develops for 38 weeks.
How do IVF transfer dates change the due date calculation?

In IVF, the exact day of fertilization is known, so the due date is calculated from the embryo transfer date rather than the LMP. For a Day 5 blastocyst, the EDD equals the transfer date plus 261 days; for a Day 3 embryo, it equals the transfer date plus 263 days. These offsets reflect the embryo's age at transfer relative to conception. IVF dating is generally considered more precise than LMP-based estimates.
Why do most babies not arrive on the due date?

The estimated due date is the average length of pregnancy, not a deadline. Only about 4–5 percent of babies are born on their predicted EDD. Roughly 80 percent of full-term births occur between 37 and 41 weeks, with the natural distribution centered around 40 weeks but spread over a four-week window. Factors such as genetics, first vs. subsequent pregnancy, and individual variation in gestation length explain why the date functions as an estimate rather than a fixed appointment.