Must be getting old - can't work this one out... :(

Want to calculate a weekly PAYG (pay as you go) tax, based on a variable
quarterly tax percentage...

1st Quarter PAYG tax percantage 12.74%
2nd Quarter PAYG tax percentage 13.12%
3rd Quarter PAYG tax percentage 13.12%
4th Quarter PAYG tax percentage 18.10%

Examples:

Pay Date Total Weekly Sales PAYG
30/11/2004 2,257.40 296.17
17/05/2005 2,574.58 466.00
07/06/2005 3,180.21 575.62

So when I enter the "Total Sales" figure, the formula matches the Pay Date
to the appropriate quarterly PAYG tax percentage, multiplies the Total Sales
by that percentage and puts it under PAYG.

I hope that this is clear enough - I used to be able to do this at the drop
of a hat, but now either the brain has slowed down or I have not had enough
practice (probably both!).

TIA

/viz