Estimate your likely conception date based on either your last menstrual period or your due date.
This tool estimates the approximate date of conception based on either your last menstrual period (LMP) or your expected due date, using standard pregnancy dating conventions. It's intended as a general estimate to help with planning and record-keeping, not as a substitute for medical dating from a doctor or ultrasound.
A full-term pregnancy is typically estimated at 266 days from conception, or 280 days (40 weeks) from the first day of the last menstrual period, since ovulation and conception usually occur around two weeks after the period begins. The calculator works backward or forward from your input date using these standard averages.
Enter either your last menstrual period date or your due date, and the tool estimates the likely conception window.
Example: If your last menstrual period began on January 1, ovulation and likely conception would fall around January 14–15, roughly two weeks later.
How accurate is this estimate? It provides a general estimate based on average cycle timing. Actual ovulation and conception dates vary between individuals and cycles, so this should be treated as an approximation.
Does cycle length affect the estimate? Yes — this calculation assumes an average 28-day cycle with ovulation around day 14; shorter or longer cycles shift the likely conception window.
Is this useful after IVF or fertility treatment? For IVF pregnancies, the actual transfer or fertilization date is more accurate than this general estimate, since exact timing is already known.
Should I use this instead of a doctor's dating? No — this tool is for general reference only. Your healthcare provider's dating, especially from an early ultrasound, is more accurate for medical purposes.
Why do due dates use 280 days instead of 266? Because the exact ovulation date is usually unknown, due dates are conventionally counted from the last menstrual period rather than from conception, adding about two extra weeks.