How do I calculate Percentages of Variables in HTML : I pretty much just started learning to code so I know only the most basic info so I might not understand too many coding terms if their put out there.

I was trying to make a variable go up by a certain percent every time you click a button. I understand how I could do most of that, I just need to know how to multiply variables with percentages.

Could anyone explain to me how to multiply variables with percentages in html.