Eleven pregnancy and fertility calculators, each named to the method behind it: Naegele's rule for last-period math, the ACOG redating thresholds an ultrasound can trigger, and published ranges for hCG rise and weight gain. Enter your dates and see the reasoning, not a black box.
From trying to conceive through your due date.
Estimated due date from your last period or conception, using Naegele's rule.
Open calculator →Track your pregnancy week by week with trimesters.
Open calculator →Your fertile window and ovulation date.
Open calculator →Estimate when you conceived from a due date or last period.
Open calculator →The due date, pregnancy, trimester and gestational age calculators run Naegele's rule: last menstrual period plus 280 days. When an early ultrasound disagrees with that math by more than the threshold set out in ACOG Committee Opinion No. 700, the scan is the one to trust, and we say so on the page rather than pretending our arithmetic wins. The hCG calculator reflects the doubling pattern described in the clinical hCG literature, and the weight gain calculator follows the National Academies' 2009 BMI-based ranges. The full source list, dated and linked, is on the editorial standards page.
Search "due date calculator" and most results give you a date with no explanation. Ours tells you it is Naegele's rule, cycle-adjusted, so you can check it by hand in about a minute.
The due date guide and accuracy guide both say plainly when an ultrasound should move your date and by how much, instead of treating last-period math as final.
Every result on this site is built from numbers that stay on your device; there is nothing to log in, no account to lose, and nothing stopping you from screenshotting a result to bring to your next appointment.