Hi guys,
I want a formula that will output how much of my weekly tax is witheld based on my weekly earnings. I'm not an accountant or anything, just someone whose **** about budgeting.

The ATO equation to calculate it is:
y = ax - b.
Where:
y = weekly tax witheld
x = gross weekly income + 99 cents
a and b = coefficients that change according to what bracket my weekly income falls into.

I have a 2 tables: tax-free threshold claimed and not claimed,with different threshold and coefficients. They look something like this:
1 2 3 4 5 6 7
A x> x< a b x y
B 0 500 0.10 10 $1200 ??
C 500 1000 0.20 50
D 1000 1500 0.30 100
E 1500 2000 0.40 150
F 2000 2500 0.45 180
G ...

Lets say my gross weekly earnings 1 week is $1200 (B6), I know that y (B7) can be evaluated using a formula like this:
=IF(AND(B6>B1,B6<=B2), B3*(B6+0.99) - B4, IF(AND(B6>C1,B6<=C2), C3*(B6+0.99) - C4, IF(AND(B6>D1,B6<=D2), D3*(B6+0.99) - D4, IF( ... and so on ))))

However, this method is extremely tedious, especially if the table exists on a separate worksheet and I have more than 1 tax table. Is there a more robust and direct method, ie treating the columns as arrays and using array operations. I also don't see the point in repeating the y=ax-b formula for every range that x could fall into as it is fundamentally the same for every tax bracket.
Any ideas? Thanks