You work out it out from the first day of your last period.
For example:
say the first day of your last period is the 1st Jan, the fertilization would take place on the 13th,14th or 15th day from then on. So you would conceive maybe on the 13th, 14th or 15th of Jan, but the most fertile day out of them 3 would be the 14th this is usually the day when the egg is released from your ovary.
This information is right if you have a 28 day cycle
It can either be calculated by the date of ovulation if you know the exact date or you can calculate by the first day of your last period.
Calculate from the 1st day of your last period.
Estimated due dates and pregnancy time lines are calculated from the very first day of your last menstrual period.
You work out how long it is since the FIRST day of you last period.
The date is calculated from the start day of the last menstrual period.
Estimated due dates and pregnancy time lines are calculated from the first day of your last period.
It depends what day your last period started. You can calculate your due date here: http://www.amazingpregnancy.com/duedate/index.html
Its calculated from the last menstrual period.Their are a lot of pages that can help to calculate how many weeks pregnant you are.
That depends on the species you are asking about. Different animals give birth after different periods of gestation.
you add 280 days to a reliable first day if your last menstrual period
To calculate an estimated due date you should count from the very first day (the day you started bleeding) of your last menstrual period.
Generally, the expected date of delivery (EDD) is calculated as 40 weeks counting from the woman's last menstrual period (or from the date of conception if known).