Pregnancy Due Date Calculator for Irregular Periods

If your periods are irregular, the standard 28-day Naegele's rule may produce a less accurate EDD. Enter your best estimate of the first day of your last period, then set the cycle-length field to your typical average (the tool accepts 21–45 days). A longer cycle moves the EDD later; a shorter cycle pulls it earlier. For cycles that vary widely month to month, note that a first-trimester ultrasound crown-rump length (CRL) measurement is the most accurate method of dating — it is routinely used to confirm or adjust the LMP-based EDD.