Hi,
I'm always finiding myself writing many varations of functions to calculate percentage.
I think it would be nice if postgresql would have build in functions for that.
I think the major functionality is something like the 3 ooptions here:
https://percentagecalculator.net/
 
It may help to keep code simple and clean and it seem like something simple to implement.
 
If you think it's a good idea it would be nice if someone can implement this.