Litigators calculate deadlines all the time. Sometimes we pull out a calendar and literally count the days to determine the date of a deadline. We can also use Excel, which is great if you are comfortable with Excel. For the rest of us, though, there's now a better option: using an online deadline calculator. There are other calculators out there on the Web, but they aren't easy to use. To calculate a date below, simply fill out the form, and you'll see your due date appear below.