All About Due Dates

Use the Gestation Calculator above to calculate your gestation, or how far along you are in your pregnancy.  Select the month, day and year of your due date in the drop box controls near the middle of the calculator and click the "Set Your Due Date" button to calculate your gestation.

The due date can be either a due date based on a last menstrual period or a due date based on an ultrasound.  The gestation will be displayed in weeks and days by default, but will be displayed in months if you select "Months" in the "Display gestation as:" section of the Gestation Calculator.  The Gestation Calculator assumes that the average length of a month is 4.44 weeks when it converts weeks to months.  Refer to Why do you use weeks instead of months? for a more detailed explanation of the difficulties (and absurdities) of converting weeks gestation to months gestation.

There are certain limitations to the due date that you can enter.  The latest due date that you can enter is 280 days from today, which would give a gestation of 0 weeks and 0 days.  Choosing a later due date would result in negative numbers for the EGA which doesn't make sense.  Therefore, if you set the due date to a date that is too far in the future, the Gestation Calculator will force the due date to a date that is no more than 280 days from today.  The earliest date that you can enter for the due date is 14 days before today.  This will give a gestation of 42 weeks and 0 days.  If you are more than 42 weeks gestation, you know exactly how far along you are and a Gestation Calculator becomes irrelevant.  Therefore, if you set the due date to a date that is more than 14 days before today, the calculator will force the EDC to a date that is no more than 14 days before today.

The Gestation Calculator will not allow you to enter an invalid date for your due date. For example, if you try to enter "February 30, 2000," for the due date, it will be forced to a legal date, i.e., "February 29, 2000."