The standard ante should represent 25% of the small blind. If the chips don't divide like that, you should veer between 20% and 33%, but no less than 20%. In this case, you could choose to go with a standard 25% of small blind ante, but instead they use a 12.5% ante.
Unlike the blinds, everyone at the table pays the ante when they are in play. Antes tend to be much smaller than the blinds and are usually between 10-15% of the big blind. For example, a tournament with antes in play may have a 500 small blind and a 1,000 big blind. Antes will likely be between 100 and 150.
