About Us

Due Date Calculator is a small, independent website offering two free tools for women who are pregnant or trying to conceive: a pregnancy due date calculator (by last period, conception date, or ultrasound) and an ovulation calculator that estimates your fertile window.

The tools follow the same methods used in everyday clinical practice — Naegele's rule for last-period dating, the 266-day count for conception dating, and back-calculation from ultrasound measurements — with adjustments for cycle length where the evidence supports them. Our explainer page shows the maths openly, because you should never have to trust a black box with a date this important.

Both calculators run entirely in your browser. The dates you enter are not sent to our servers, not stored in a database, and not shared with anyone. We think the beginning of a pregnancy is personal, and our tools are built to keep it that way.

The site is free to use. We may earn a small commission when visitors buy products through Amazon links on our pages (for example ovulation test kits or prenatal vitamins), at no extra cost to the buyer. That is the site's only income, and it never influences the calculators' results. See our Affiliate Disclosure for details.

We are not doctors, and this site is not a medical service. The calculators provide estimates for general information only. Your own doctor or midwife — who can examine you and read your scan results — is always the final word on your dates and your care.