Pregnancy Calculatorcalculate your due date Pregnancy Due Date Calculator First Day of Last Menstrual Period* first day of bleeding. required field Average Length of Cycles From first day of your period to the first day of your next period. Ranges from: 22 to 44. Default = 28. Optional: Leave 28 if unsure. Calculate! Estimated Fertility Window thru Estimated Conception Date Estimated Gestational Age Estimated Due Date This is not a diagnosis. The calculations that are provided are estimates based on averages.