I have been asked to create a "deposit relationship calculator" in excel. We would like our CSR's to input the customers balances on deposit accounts and the rate we are paying them. This calculator would then provide an average weighted rate we could offer that customer on a new account. If the customer is rate shopping, we wanted a way for our CSR's to be able to make the decision.

Are you just looking for the formula to calculate the average weighted rate?

yep....I thought excel would have a function to do this, but it doesn't

I found something for loans (I would imagine deposits works the same). I'll PM you.