|MadSci Network: Astronomy|
You are correct for the most part. There are some fractions of a day that are unaccounted for, and so we make up for this lost time by including Leap Day in February, roughly every 4 years. More information about Leap Day (and Leap Year) and why we have it can be found at The Royal Observatory of Greenwich's Leap Year site and the Leapday/Leap Year site.
Information about minute calibrations involving the Leap Second can be found at the US Naval Observatory.
[Moderator: To be more complete, one must also specify the kind of year in which one is interested.]
Try the links in the MadSci Library for more information on Astronomy.