Question

why interest rate is always in percent?

Answer 1

What else would make sense?

Answer 2

Because interest is just taking a percentage of what you owe.

Common example is credit card interest rate.
If you spent $100 on credit card you bill will be $100, if you don't pay you get charged an interest rate.

That interest rate could be 8% of what you spent. So $108

Answer 3

thats fine, my point is why its always in percentage and not in other denomination, say 13/26 is also 50%, but why we consider 100 base always, and if we consider, other base, will it make any difference in compounding formula A=P(1+r)^n

Answer 4

It makes no difference with regards to computation.

It's just how we humans communicate, because our number system is base 10 we tend to relate everything to 10s.

You wouldn't say, " I have 'one and one fifteenth of a dollar'"? Would you?

You'd make more sense of it in the real world if you just said you had a penny.
It's all about what's easier to convert in your head and what the standard is within your society.

Sort of a big reason why the metric system in the U.S. is HORRIBLE!!
We can easily from cm to m to km...
But from
inches to feet to miles to whatever comes next is just a pain.

base 10 is where it's at.