Enter your due date to work backward and estimate your likely date of conception, along with a conception window and the corresponding last menstrual period date.
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This calculator works backward from your due date using the standard 266-day gestation period counted from conception (as opposed to the 280 days counted from your last menstrual period, which includes about two extra weeks before ovulation). It also shows a small conception window around that date, and the corresponding last menstrual period date for reference.
The Pregnancy Due Date Calculator works forward, from your last period to your due date. This calculator works in the opposite direction, from a known or expected due date back to an estimated conception date, useful when you know your due date but want to estimate when conception likely occurred.
Conception can't be pinpointed to an exact day from a due date alone, since ovulation timing varies. The window reflects a few days of typical uncertainty around the calculated estimate.
Yes, you can enter the actual birth date in place of a due date for a similar backward estimate, keeping in mind that babies aren't always born exactly on their due date.
This calculator works backward from a due date to estimate conception. The Pregnancy Due Date Calculator works forward from your last period to estimate a due date. They're inverse calculations.
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