Due Date Calculator by Conception Date
Enter your conception date to see your estimated due date, 266 days later.
Conception-date due date — no upload, no accountEstimates only — not medical advice. Confirm all dates and milestones with your doctor or midwife. Read our full disclaimer.
How this due date is calculated
Enter your conception date. Your due date is 266 days (38 weeks) after conception, because pregnancy is measured from about two weeks before conception.
Counting from conception instead of LMP removes the roughly two-week "pregnancy before pregnancy" gap. In a natural cycle the egg is fertilized about 14 days after the last period, so the due date is 266 days out rather than 280. This method is most trustworthy when ovulation or insemination was actually tracked, because the conception day is then known rather than inferred from a period you may only roughly remember.
What to expect
The conception date is the day fertilization happened. Because pregnancy is measured from the last period (about two weeks earlier), a due date calculated from conception adds 266 days (38 weeks) rather than 280.
You might know your conception date if you were tracking ovulation, using an ovulation predictor kit, or went through a monitored cycle. In those cases a conception-based due date can be more accurate than an LMP-based one, since it does not depend on remembering the exact first day of a period.
Example: a conception date of January 15 gives an estimated due date around October 8 — the same ballpark as an LMP of January 1, because LMP is roughly two weeks before conception.
If you are not sure of the exact day, a range is fine for planning. An early ultrasound remains the most reliable way to set an official due date, especially when the conception date is uncertain.
Note the difference from "last period" calculators: this tool asks for the conception day itself, not the first day of your last cycle, so do not mix the two up when entering a date.
Important note
These calculators use standard formulas — Naegele's rule (LMP + 280 days) and common IVF conventions (transfer date + 260–263 days). They give estimates for planning only. They are not a substitute for prenatal care, and only your provider can confirm your due date and track your baby's development. See the disclaimer for details.
FAQ
What is my conception window?
The fertile window is roughly five days before ovulation through one day after. If you know approximately when conception occurred, enter that date; your due date is 266 days later.