Calculating different tax levels

I would very much appreciate help with trying to work this out. I’m trying to develop a number of databases using Filemaker Pro 9 Adv for a ministry in Kosovo.

One aspect that I’m trying to automate for budget and personnel purposes is to show deductions on salaries for income tax.

It works like this:

There are four levels.

After a gross salary there is a deduction for pension contributions (that I’ve worked out it’s a simple calculation and I have a field to capture the result).

After that there are the income tax deductions.

These are for the first 80 euros the rate is 0

From 80.01 to 250 it is 5%

From 250.01 to 450 – 10%

Above 450 - 20%

For info these are monthly figures

My question is can I use an IF or CASE function using the calculated result field that I have as mentioned, that would in effect find the different ranges within the number, and if so what would the formula be. I’ve looked around for a solution and have been racking my not terribly mathematical brain and thus far, have not come up with the solution.

Any advice would be extremely valued

Thanks

John