There is no such thing as year 0, so if a century is every 100 years – the first century would be from year 1 to year 101. Following that pattern, every century starts with 01. For example: The 19th Century started on January 1st, 1801.
As someone who loves history, I am quite shocked it took me this long to find this out!
Source: The Library of Congress – “When does the century end…“