Due Date from Conception Calculator
Find your due date from the date you conceived (conception + 266 days), with weeks pregnant on any date, trimester and key pregnancy milestones.
Use an estimated fertilization date to calculate a due date 266 days later and gestational age on a chosen day. Intercourse, an ovulation test and an IUI date do not establish the exact fertilization day. The equivalent last-period date is a dating convention, not a claim about when bleeding occurred.
How to use this tool
- Enter the best available estimated conception date; follow your clinic’s dating for an IUI pregnancy.
- Leave "Show progress as of" on today, or pick another date to see how far along you will be then.
- Read the due date, gestational age and the milestone table.
Formula
Due date = conception date + 266 days · Gestational age = (chosen date − conception date) + 14 days
Obstetric dating counts from the first day of the last menstrual period (LMP). In a textbook 28-day cycle that falls 14 days before ovulation and conception, so 266 + 14 = 280 days — the standard 40 weeks. Trimesters are split at 14 weeks 0 days and 28 weeks 0 days; full term is 39 weeks 0 days to 40 weeks 6 days.
Example
Conception on January 15, 2026 gives a due date 266 days later: October 8, 2026. The equivalent LMP is January 1, 2026, and Naegele's rule from that date (add nine months and seven days) lands on the same day. On April 15, 2026 the pregnancy is 14 weeks 6 days — in the second trimester — with 176 days to go.
Frequently asked questions
How accurate is a due date from conception?
It is only as good as the conception date. Sperm can survive up to five days, so the day of intercourse is not always the day of conception; ovulation tests or temperature charts narrow it down. Even with exact dating, most births happen somewhere between 37 and 42 weeks.
Will my doctor use this date?
Usually the due date is set from your last period and confirmed or adjusted by a first-trimester ultrasound. If the scan differs by more than a set number of days, the scan date is used instead.
Why am I "2 weeks pregnant" on the day I conceived?
Because pregnancy has long been counted from the last period, the date most people know. By that convention the first two weeks pass before conception happens.
Sources
This tool gives an estimate for general information only. It is not financial, tax, legal or medical advice — check with a qualified professional before you rely on the result.
Last updated: 2026-10-30