A pregnancy calculator can give you an estimated due date when you know the first day of your last menstrual period and your usual menstrual cycle length. That date is useful for understanding the expected pregnancy timeline, but it is not a prediction of the exact day your baby will be born. Cycle regularity and certainty about the last period date can affect how closely a calculator estimate reflects clinical pregnancy dating.<\/p>\n\n\n\n
Key takeaway:<\/strong> The pregnancy calculator estimates your due date from the first day of your last menstrual period and your average cycle length. Pregnancy is commonly dated from the start of the last menstrual period, with an estimated due date around 40 weeks later. The result is an estimate, and the date may be revised when menstrual dates are uncertain, cycles are irregular or clinical assessment gives a different pregnancy dating estimate.<\/p>\n\n\n\n Enter the date your last period started and your usual cycle length into the existing calculator. Use the result as a pregnancy-timing reference rather than as an exact birth-date prediction.<\/p>\n\n\n\n