How do you convert 1977 ACT scores to current scores?

You can't directly convert a 1977 ACT score to a current ACT score with a simple formula. The scoring system, test content, and difficulty have all changed significantly over the years. There's no official conversion chart provided by ACT.

Any attempt to convert would be an approximation at best, and would likely be unreliable. The changes in the test make comparing scores across such a large time span inherently problematic. Instead of trying to convert, it's more accurate to simply acknowledge that a 1977 score is not directly comparable to a modern ACT score.