Due Date Calculator

We add 280 days (40 weeks) to the first day of your last period, then adjust by the difference between your average cycle length and 28 days. For example, a 30-day cycle adds two days. The conception estimate uses ovulation 14 days before your next expected period.

The weeks, days, and trimester shown are counted from your last period, without a cycle-length adjustment. The due date is cycle-adjusted, so it may not coincide with exactly 40 weeks on this display. The percentage is elapsed calendar time toward that date, not a measure of fetal development or pregnancy health.

This tool accepts cycle lengths of 21–35 days. An uncertain last period or irregular cycles makes the estimate less reliable; do not enter a substitute cycle length. Ask your clinician about ultrasound dating. For IVF or other fertility treatment, use the dating provided by your clinic.

An early ultrasound may refine the estimate. First-trimester ultrasound is the most accurate method to establish or confirm gestational age. Once your clinician sets a due date, later scans do not routinely change it.

Gestational age is conventionally counted from the first day of the last period. Conception age starts at fertilization, usually about two weeks later in a 28-day cycle. The gap varies with ovulation timing. This tool estimates the conception date from the calendar; it cannot identify the actual date of fertilization.

No. A due date is a reference point for pregnancy dating, not a scheduled birth date. Birth can occur before or after it. The countdown shows days until the calculated estimate; reaching zero or 100% does not mean labour has started or indicate whether the pregnancy is healthy.