Formula for calculating GST

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Formula for calculating GST



Quick...I haven't done this in a long time.

Say you only have the full amount paid, but you want to calculate how much of that is GST. What's the formula?

So, in my case, a receipt is for $50. I need to know how much of that is GST and it doesn't show on the receipt.

I know it has to do with multiplying by 106 and then dividing by 100 or something like that, but I can't remember the exact formula. Help!


Okay, I figured out a short way of doing it and tested it on $53 which is easy.

Divide $53 by 106. You get $50.

So I did that with $50, and I got $47.17. So the remainder ($2.83) is the GST.

But I KNOW there's another easy formula that gets you there without having to do the subtraction thing, and I can't remember it! It's going to make me nuts until someone tells me! And you don't want a nutty moderator running around.


This is for Ontario only.

If an item is changed GST only, multiply the final cost by 0.0566 to find the GST amount (6/106=0.0566).

If an item is changed PST only, multiply the final cost by 0.0741 to find the PST amount (8/108=0.0741).

If an item is changed both GST and PST, multiply the final cost by 0.0526 to find the GST amount (6/114=0.0526) and by 0.0702 to find the PST amount (8/114=0.0702).

It helps if you have a calculator.

Bobolink Bobolink's picture

This is the rule of reciprocals. Multiply a number by the reciprocal of 1.06 which is .0567 and you will get a number that is 6% of the original cost.

Krago beat me to it and his explanation is more eleoquent.

[ 25 April 2007: Message edited by: Bobolink ]


I talked to Rev Can about this. Apparently there's an even simpler method.

Change your name to Bronfman, and you don't have to worry about tax at all.

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I've always found it easier to solve problems like this by reversing the method used to add the tax.

If multiplying a price by 1.06 gives you the price + tax then dividing the total by 1.06 will give you the price without the tax.


The GST is 6% correct?

The amount paid for the GST is 6/106*100% = 5.66%.

So just multiply the bill by 0.0566, and that's the amount you paid in GST.


Chiming in late on this one, but I found this thread through Google so assuming there are others like me.

My example is for parking that cost me $9 and I need to know how much I paid for GST (Canada's Federal Goods & Service tax which right now is 5%).

Here is how I did it:

$9 divided by 1.05 = $8.57.
This is the total I paid not including GST. So then I did the basic subtraction of:
$9 minus $8.57 = $0.43 GST

To do this in Excel the formula would be


M. Spector M. Spector's picture

Or conceptually easier:




Originally posted by M. Spector:
[b]Or conceptually easier:


or one step further:



Now is that celcius or fahrenheit? [img]wink.gif" border="0[/img]


proof that people inclined towards bending their noodles around social and political phenomena tned strongly towards the numerically challenged.

rural - Francesca rural - Francesca's picture

That's because we're trying to do $1 millon worth of good works with $100 000

Boom Boom Boom Boom's picture

A friend wrote on my Facebook page that the feds are considering cancelling GST rebates this year. First I've heard of this! Can anyone confirm this, or is it just an unsubstantiated rumour? (the GST rebates benefit folks on low incomes - like me)

G. Muffin

Boom Boom, I just received my rebate.  It was $106.63 including the Carbon Tax Rebate.  Do you want to know how I spend $106.63 quarterly?  The programs costs more than that to run -- it's a loser.  I realize that we need bureaucrats.  Otherwise, the EI system would collapse under the weight of the influx.  Same reason we need academics.  But, seriously, do we need this?  The only benefit that lower income folks need is a higher income.  $1.17 a day doesn't qualify.

Boom Boom Boom Boom's picture

I'd love to see the GST dropped entirely, but as long as it's a reality, I'd still like my refund. That $100+ quarterly buys an extra couple of bags of groceries four times a year.

G. Muffin

I hear you, Boom Boom.  I don't exactly sneeze at it; I just don't think it's an effective poverty protection, I guess.

G. Muffin

Fair enough, Boom Boom.  I agree it should stay.

Boom Boom Boom Boom's picture

Oh, I agree - I'd like to see the feds tackle poverty in a way that makes a difference. In the meantime, if they take the GST rebate away, that's another $400 or so from the pockets of the poor.


ETA: is the gov't really planning to end the GST rebates?

George Victor

And if they had not  cut the GST by 2 per cent, there would be even more rebates. The cut in GST aimed at getting the Cons re-elected, chopped $16 B off federal revenues, more than one quarter of the year's deficit.

The rebate should "stay" and be added to.

G. Muffin

I concur, George Victor.

Don't all well-meaning roads lead to a universal guaranteed income? 

If I need (and I do) a new pair of runners, what does it profit me to know that my next band-aid is due in April?


I have made one excel sheet and put the excel formulas to calculate the GST, PST or both. As Krago suggested just multiply the price by 0.056 for GST, 0.0741 for PST, and if charged both multiply by 0.0526 for GST and 0.0702 for PST.  excel formulas makes it very easy to calculate, just put the actual price and you have all the values.



Total divided by 1.05 ( for a 5 percent tax ) equals the purchase price, difference is the tax.