Due Date Calculator by Conception Date

This page opens the due date calculator with the conception-date method already selected: enter the day you believe conception happened and the estimated due date appears immediately, together with milestone dates for weeks 12, 20, 28, and 37. Counting from conception adds 266 days (38 weeks) — the average length of pregnancy measured from fertilization rather than from the last period.

The conception method is useful when you know the timing with reasonable confidence — for example, from ovulation tracking, basal temperature charts, or a single possible date in the cycle. It skips the assumption that ovulation happened on day 14, which is where the classic last-period method can drift by several days for longer or shorter cycles. Keep in mind that sperm can survive up to five days, so even a known date of intercourse is not always the exact date of fertilization.

Pick the date and read the result — nothing is uploaded, and the calculation happens entirely in your browser. If you only know the first day of your last period, switch the method selector back to that mode. The result is an estimate for orientation, not medical advice: an early ultrasound remains the most accurate way to date a pregnancy.