[AccessD] A2003:Calculating Percentages - and their currency values

Darren:

To find out any included percentage, simply divide by 1 plus the percentage
in decimal form.

If the tax rate (TR) was 12.5% and the tax included value (TIV) was $146.24,
divide by 1.125 to give you an original net price (ONP) of $129.99. You
obviously will have to dealing with rounding factors, but you will always be
within 1/2 of 1 cent ($0.005) with this formula.

ONP = TIV / ( 1 + TR)
ONP = $146.24 / ( 1 + .125 )
ONP = $146.24 / 1.125
ONP = $129.99

To determine just the amount of the tax (TA), divide by one plus the
percentage in decimal form and then multiply the result by just the
percentage in decimal form.

TA = (TIV / ( 1 + TR)) * TR
TA = ($146.24 / ( 1 + .125 )) * .125
TA = ($146.24 / 1.125) * .125
TA = ($129.991111) * .125
TA = $16.248889 or $16.25

or

TA = ONP * TR
TA = $129.99 * .125
TA = $16.24875 or $16.25

The first example is more accurate because you do not lose any precision to
rounding until the final step.

HTH

Bob Gajewski


-----Original Message-----
From: accessd-bounces at databaseadvisors.com
[mailto:accessd-bounces at databaseadvisors.com]On Behalf Of Darren DICK
Sent: Saturday, January 15, 2005 09:52
To: 'Access Developers discussion and problem solving'
Subject: [AccessD] A2003:Calculating Percentages - and their currency
values


Hello all
In Australia we have a sales tax apply to all purchases. It's called GST
(Like VAT in Britain)

At the moment the Govt. has set this Tax at 10 percent. Makes the maths very
simple by
Just adding 10 percent to each currency amount.

To calculate any TAX inclusive amounts we just divide the grand total by
1/11 (one eleventh)

So far so good.

Until the Govt. changes the GST Rate (they said they won't but we all know
they eventually will)

So I don't want to hard code "Divide Grand total by one eleventh" to get any
GST inclusive amounts.
If the GST amount is changes to say... 12.5 per cent - it won't work -
obviously

So.for all the mathematically inclined folk out there..
Is there a clever formula for working out GST Inclusive prices regardless of
the Current TAX rate?
Just like the one eleventh business works for 10 percent?

Many thanks

Darren
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