How Do I Know Which Century?

1601 would be the 17th century
1701 would be the 18th century and so on...
You just add one to the year to get the century =)

A century is 100 years. We had no year 0 so the first century was years 1-100 and the second century was years 101-200. So the Century always sounds like it is one ahead of the 100's number of the year. But the 21st century really is from year 2000-2099.