Sliding Scale Commission

Hello,

I wonder if someone would help me with sliding scale commission, :-( I have created this spreadsheet that is to calculate commission (on Sliding Scale basis), however, I can not create a formula that will give me the exact commission rate between scales.. for example, between 0 - 50k our consultant will receive 10% commission and from 50K - 100K 15% commission - but if the consultant bills 57k I need my spreadsheet to calculate 10% on the 1st 50k and 15% on the 7k..

So basically this is way beyond me..I could easily do this on a calculator but would like a spreadsheet that tally's this all up for me..

Please please would someone help me, I am going out of my mind with IF's and SUMS and all other functions..

Attached is an example of my spreadsheet.

Thanks for your help