Reverse Due Date Calculator

Your details

Reverse mode: enter due date and get conception date. Forward modes: enter conception or LMP date and get due date.
The estimated delivery date, or the actual birthday if the baby has already been born.
Used to refine the ovulation offset. The standard assumption is 28 days. For longer or shorter cycles the conception estimate shifts accordingly.
days
Estimated conception dateSecond trimester
Sat, Apr 4, 2026

The most likely date of ovulation / fertilisation

Intercourse window - earliestMon, Mar 30, 2026
Intercourse window - latestMon, Apr 6, 2026
Estimated due dateSat, Dec 26, 2026
Last menstrual period (estimated)Sat, Mar 21, 2026
Gestational age today20 weeks 0 days
Days until due date140 days

Estimated conception: Sat, Apr 4, 2026

  • Working back 266 days from your due date places conception around Sat, Apr 4, 2026.
  • The intercourse window that most likely led to this conception runs from Mon, Mar 30, 2026 to Mon, Apr 6, 2026.
  • As of today this pregnancy is approximately 20 weeks 0 days by gestational age (counted from LMP).
  • Conception timing is an estimate. Sperm can survive 3 to 5 days inside the reproductive tract, and ovulation timing varies, so a range of dates is always more accurate than a single day.

Next stepFor a definitive conception date, an early ultrasound (7-10 weeks) can pinpoint gestational age to within 5-7 days.

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