How long is a goat pregnant?
Goats are pregnant for about 150 days, roughly five months. Most does kid between day 145 and day 155. Smaller breeds such as Nigerian Dwarfs often kid toward the shorter end, and does carrying twins or triplets tend to kid a little earlier than does with a single kid.
The calculator counts 150 days from the breeding date. If the buck ran with the does for a while, use the first day you saw her mated, or the middle of the time they were together, and watch her from day 145.