Blinds & Antes confusion
Using Roberts Rules an ante is defined as


  A prescribed amount posted before the start of a hand by all players.


So the ante has no effect on the amount paid by blinds.  Each player posts there ante before the hand starts.  These chips are then moved to the pot and its in effect 'dead money'  it has no bearing on how much players play in blinds.

I'm not aware of a hard and fast formula for calculating an ante in live tournaments its roughly the size of the big blind divided by number of players max at a table.

so in live games I've played is Big blind in 200 the ante is usually 25.  This will probably vary from game to game and casino to casino.

In recent games I've played the rules have changed to the Big Blind or button posting the ante for all players.  

So if the rules are "button antes" and the blinds are 100-200 the button also posts 200 before the hand begins.  The advantage of doing this is speeding up the time takes to take the antes in rather than every player all posting the same amount each time, invariably one player always having to be reminded and change sorted if needed.