Add percent to numbers

Question

How can I add percent to a sum? I have tried var sum = 3.25 + '3.4%'; but it didn't work. I'm just getting 0.00 as an answer.

Answer 1

To "add a percent to a number" means "multiply the number by (1 + pct)":

var sum = 3.25;
sum = sum * (1 + 0.034);

You could equivalently skip the 1 (that's just the way I think about it) and add:

var sum = 3.25;
sum += sum * 0.034;

So if you're starting off with a string representation of a percentage, you can use parseFloat() to make it a number:

var pct = "3.4%"; // or from an <input> field or whatever

pct = parseFloat(pct) / 100;

The parseFloat() function conveniently ignores trailing non-numeric stuff like the "%" sign. Usually that's kind-of a problem, but in this case it saves the step of sanitizing the string.

Answer 2

The simplest method is to use arithmetic operators.

var sum = 3.25

sum += sum *= 0.034;

< 3.3605