Are you or your partner pregnant? if you know (or can guess) when your baby is due, you can instantly calculate how long to go or which week you are in. The calculation also lets you easily work out the trimester you are in. The gestation method is where you take the 40 weeks of gestation and divide into three equal stages. First trimester is anything before 13 weeks and 3 days. Second trimester begins at 13 weeks and 3 days and the third at 26 weeks and 6 days. Simply choose the due date from the calculator on the homepage or navigate to the date by clicking on the year, month then day and you’ll get a page with all the countdown answers you need. You can even set a reminder, this will email with a countdown.