You can use apps, My Day and Countdown, from Google Play to create a countdown clock to measure time in days. iTunes provides the apps, Countdown!! and Countdown Timer Pro, for use on an iPhone or iPad.
CountingDownTo.com offers a countdown widget you can affix to a website. Timeanddate.com allows you to create a countdown and share the link with friends or family. Commonly, people count down to holidays, birthdays, weddings, vacations and baby due dates. Countdown apps work well to help people manage time and stick to deadlines. The apps also build excitement and anticipation around a special event. Countdown apps come with themed backgrounds to fit many different occasions.