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Best practise is to have parameters on the worksheet, not in a formula. So, when parameters change you don't need to modify formulas - just enter the new parameters. Therefore

```
[B1] = Lower tax bracket start
[B2] = Lower tax rate (%)
[C1] = Upper tax bracket start
[C2] = Upper tax rate (%)
[A4] = Taxable amount
```

After this preparation the formula below will work out the tax payable for any amount entered in column A. You can copy the formula down from its original position in row 4.

`=(MAX(($A4-$C$1)*$C$2,0))+(MIN((MAX($A4-$B$1,0))*$B$2,$B$1*$B$2))`

Of course, you can place the parameters anywhere on your sheet and change the formula to point to the cells you prefer. That's a one-time change. Similarly, you can place the parameters in named ranges (cells) anywhere in your workbook and replace the sell references in the formula with the names you assign. Either way is good practise.

Less good, but more common, is to replace the cell references B1, B2, C1 and C2 in the formula with actual numbers. That will work, too, but it will cause you more work whenever the parameters change.