Due Date Calculator

Written by Great Medico

Updated September 24, 2026 •2 min read

Share Print Save

Small timing differences can change how pregnancy and fertility numbers are understood. Due Date Calculator applies one defined method to the values you enter so you can see what the calculation actually means.

What this calculator does

Due Date Calculator uses Method, My last period started on, My average cycle lasts, and Conception date to calculate due date. It is built around the exact fields displayed in this plugin rather than a generic version of the topic. Pregnancy and fertility dates, hormone trends, and risk scores are estimates built around biologic averages. Cycle variation, ultrasound findings, assisted-reproduction details, and the individual pregnancy can matter more than a single calculated number.

How to use it

Enter or select Method, My last period started on, My average cycle lasts, and Conception date. Use the units offered by the calculator and choose the option that matches the actual clinical or timing situation. Check date entries and laboratory units before relying on the output. For paired dates or serial measurements, keep them within the same menstrual cycle, pregnancy, or treatment episode as the calculator requires.

How the calculation works

For an LMP-based estimate, the calculator adds 280 days and adjusts for cycle length by adding cycle length − 28. If conception date is selected instead, it adds 266 days. The result is one estimated due date, reflecting the dating method selected in the form.

Example

For example, an LMP of January 1 with a 28-day cycle produces an EDD about 280 days later. A 32-day cycle shifts the calculator four days later because the tool adds cycle length minus 28.

How to interpret the result

Treat the output as estimated due date based on the assumptions encoded in this calculator. It can help with planning or understanding a measurement, but pregnancy and reproductive biology vary enough that the calculated date, ratio, or probability should be seen as a range or estimate rather than a guarantee.

Limitations and notes

A due date is an estimate, not a predicted birthday. LMP dating assumes the entered cycle reflects ovulation timing; first-trimester ultrasound is generally the most accurate method to establish or confirm gestational age, and IVF pregnancies should use ART-derived dating.