Use this free online conception calculator to estimate when you likely conceived, based on either your due date or the first day of your last menstrual period. Select what information you know, enter the date, and get an instant estimate of your conception date along with a related pregnancy date. This tool is for general informational purposes only and is not a substitute for medical advice.
How to Use the Conception Calculator
Choose what you know from the "What do you know?" dropdown - your due date or your last menstrual period (LMP) date.
Enter the corresponding date in the date field.
Click "Calculate Conception Date" to see your estimated conception date.
Frequently Asked Questions
If you enter your due date, the calculator subtracts 266 days to estimate conception and 280 days to estimate your last menstrual period. If you enter your LMP date, it adds 14 days (an average ovulation point) to estimate conception and 280 days to estimate your due date.
Because conception, LMP, and due date are all mathematically related, the calculator shows the secondary date so you can cross-check your pregnancy timeline in one place.
The estimate assumes a typical 28-day menstrual cycle with ovulation around day 14, so actual conception can vary by a few days depending on your individual cycle length, as noted beneath the result.
If the date field is left blank or contains an unrecognized date, the calculator displays an error message asking you to enter a valid date instead of calculating a result.