Correction: The -0.01 should have been -0.04

In article ,
JE McGimpsey wrote:

One way:

=SUMPRODUCT(--(A1={0,15000,25000,50000},A1-{0,15000,25000,50000},
{0.15,-0.05,-0.05,-0.01})

See

http://www.mcgimpsey.com/excel/variablerate.html

for an explanation and a more flexible table-based method.