I have a tiered fee schedule and I'm trying to calculate an IF formula to
capture the different levels. Here are my conditions for an account balance
example:

My Account balance is $1000 (C1)
A: Bill 2% (A1) for the FIRST $250 (B1)
B: Bill 1% (A2) for the NEXT $500 (B2)
C: Bill 0.5% (A3) for the NEXT $750 (B3)
D: Bill 0.25% (a4) THEREAFTER

Based off my fee schedule, my bill should be $11.25 --
((A1*B1)+(B2*A2)+((C1-(B2+B1))*A3)). But this formula wouldn't work if C1
was $200, $450, $1600, etc.... What's the correct IF formula? Any help
would be appreciated