How to find the variation between two numbers

I have two numbers, one is an actual value. The other is an estimated value. I want a formula that will show me as a percentage, how much the estimate is away from the actual value.

I know it's simple and I've tried umpteen variations on formulas, but all are incorrect.

Will someone please put me out of my misery and point out the junior school maths to do this?

Thanks

Assuming your estimate value in b3 & actual value in b2.

=sum(b3*100/b2)-100

Try this. See attached.

Thanks for both your responses. Pleased to say it works... knew it was something simple. But just to make it more complicated than it needs to be, I've modified it to...
=IF(ISERROR(SUM(M74*100/L74)-100),"",(SUM(M74*100/L74)-100))
It just keeps the unfilled rows clear of errors.

Thanks again!