How to Calculate the Effect of Bonus Time
After you've played in Live Chess for a few days or more, you recognize that there are three separately rated game types: Quick, Blitz, and Long. You also note that time controls of 1 0 and 2 0 games are Quick, that 3 0 through 14 0 are Blitz, and 15 0 and beyond are rated as Long games. So far, so good.
But what about 2 12, where the 12 provides for 12 bonus seconds after each move? It is Quick? No, it's not. It's Blitz. How about 3 17? How about 3 18? Yes, these are very odd time controls, but wouldn't you like to know how to tell which times controls yield what type of game?
Effective Time, minutes = Minutes + 2/3 * (Bonus Seconds), in minutes.
Thus, 2 12 is really 2 + 2/3 * 12 = 2 + 8 = 10 effective minutes, thus Blitz.
And 3 18 is really 3 + 2/3 * 18 = 3 + 12 = 15 effective minutes, thus Long.
My favorite time control is 10 7, or 10 + 2/3 * 7 = 14 minutes, thus Blitz.
So, by using this formula you can create the exact kind of time control you want (lots of base time versus lots of bonus time) and make sure that the effective time fits into the rating group you want it to.
Have fun. And Quick/Blitz/Long yourself to some sweet chess.
(BTW: Sometimes lag correction can look like the action of bonus time even for games with no increment.)