When Republicans talk about ACA's tax increases, most of them are talking about all the taxes in the bill, not just the penalty. But they're still off base. There have been 15 tax increases of significant size since 1950, and Jerry Tempalski, a tax analyst in the Treasury Department, has estimated the size of all of them as a percentage of GDP. Tempalski hasn't estimated the eventual size of ACA, but PolitiFact took a crack at it using the same methodology, and they figure that ACA amounts to a tax increase of 0.49% of GDP seven years from now. That places it tenth on the list.