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GST & VAT Calculator

Add GST or VAT to a price, or work out how much tax is inside a price that already includes it.

$
%

Australia 10, New Zealand 15, UK 20

Tax to addWhen the amount is before tax
$100
Total including tax
$1,100
Tax inside the amountWhen the amount already includes tax
$91
Amount before tax
$909

What this assumes

  • One flat rate on the whole amount. Common standard rates: Australia GST 10%, New Zealand GST 15%, UK VAT 20%, Canada GST 5% (HST 13–15% in some provinces). US sales tax varies by state and city.
  • Whether you must register for and charge the tax depends on your turnover and your country’s rules. This works out the sum; it is not tax advice.

Why this number matters

Two sums come up on almost every job. Quoting, you know your price before tax and need the total the customer pays: multiply by one plus the rate. Reading a supplier’s invoice or a tax-inclusive price, you need the tax inside it: that is not the rate applied to the total, which is the common mistake. For a 10% tax, the tax inside a total is one eleventh of it, not a tenth; for 15% it is three twenty-thirds; for 20% it is one sixth. Getting this wrong on a quote either gives the tax away or overcharges the customer, and on a tax return it misstates what you owe.

Rates checked on against Australian Taxation Office, Inland Revenue (NZ), GOV.UK and Canada Revenue Agency. Check with your tax authority before relying on a rate.

How it is worked out

  • Tax to add = amount × rate
  • Tax inside a tax-inclusive amount = amount − amount ÷ (1 + rate)
  • For 10%, the tax inside is one eleventh of the total; for 20%, one sixth

The same formulas run in your browser as you type; nothing you enter is sent anywhere.

Invoicing in Primemgr

Turn an accepted quote or a finished job into an invoice in one click, and see what each customer still owes. Invoicing: how it works.

Start free trialSee pricingCard needed. First charge on day 14.

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