I need to be able to calculate a commission as follows:

Total Amount=$500
Total Commission (0-$100, 5%)+($101-399, 10%)+(>$400, 15%)

This would calculate a different percentage for each of the ranges
above and then add them together.  I hope I'm making myself clear
because I'm confused just writing this.

It seems like there should be a very easy way to do this in Excel.

Any assistance would be most appreciated.

Thanks,
Andy