Yes, it's outdated (since season 15). It gives decent numbers except for huge salaries (above 250-300k or something) where it is pretty off. Still useful to roughly predict salary increases for example.
But the reason why I decided to post this tool here is because it can calculate if a player has reached his potential. That's only possible since Josef Ka discovered the formula a couple of weeks ago.
"Air is beautiful, yet you cannot see it. It's soft, yet you cannot touch it. Air is a little like my brain." - Jean-Claude Van Damme