How do you calculate winning percentage with a tie game?

It depends on the sport and how ties are used. I would use point percentage rather than winning percentage to see which team has a better record. First determine how many points a win is worth and a tie.

In NHL hockey, wins are worth 2 and ties are worth 1 point. So for example, a record of 5 wins, 2 losses, 3 ties results in 13 points out of a possible 20 for a .650 point percentage. A team with 5 w, 1 L, 3 t results in 13 points out of possible 18, which is .722 percentage.

If you really need to get a winning percentage, try making ties worth 1/2 a win or just drop the ties from the record. So an NFL football team with a record of 8-7-1 is going to have a better winning percentage than an 8-8 team no matter which way you calculate... 8.5/16 or 8/15