Reverse Due Date Calculator
Know your due date but want to find your conception date or LMP? Enter your estimated due date below and our calculator works backward.
Reviewed by Pregora Editorial Team · Last updated 2026-04-26
Tip: Select "Already know due date" in the calculator below to use it in reverse mode.
Monday, December 7, 2026
224 days to go
Important: Only ~5% of babies are born on their estimated due date. Most healthy pregnancies deliver between 37 and 42 weeks.
Frequently asked questions
How does a reverse due date calculator work?▾
It works backward from your estimated due date to calculate your conception date and last menstrual period (LMP). The formula: LMP = due date − 280 days. Conception date = LMP + 14 days (assuming 28-day cycle).
Why would I use a reverse due date calculator?▾
Common reasons: (1) figuring out approximate conception date when you only know your due date, (2) identifying timeline of pregnancy events, (3) confirming pregnancy dating against IVF or fertility tracking records.
How accurate is reverse due date dating?▾
It's as accurate as the due date itself. Since LMP-based due dates assume a 28-day cycle, irregular cycles introduce some variation. Ultrasound-confirmed due dates are most accurate.
Can I find out the exact conception date?▾
Not exactly — conception happens at ovulation, which is around day 14 of a 28-day cycle. The conception 'date' is technically a 24-hour window. Sperm survival adds another 5 days of possible intercourse window.
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