GST calculator
Add tax to a price, or work backwards from a tax-inclusive total to find the base amount. The reverse direction is the one people get wrong, because you cannot simply subtract the percentage.
Built and checked by Mubashir, who works in accounting and finance. Formula and sources shown below. Not financial advice.
Amount and rate
Price including tax
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Base amount
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Tax
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Total including tax
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Show the working
The calculation with your figures substituted in:
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Adding tax and removing it are not symmetrical
This is the single most common error in tax arithmetic, and it costs businesses real money on invoices.
Adding is intuitive. A net price of 1,000 with 18% tax becomes 1,180. Multiply by 1.18.
Removing is where people go wrong. Given a gross price of 1,180 including 18% tax, subtracting 18% gives 967.60 — which is wrong. The percentage was applied to the smaller base figure, not to the total, so you must divide rather than subtract. The correct base is 1,180 divided by 1.18, which is 1,000.
The gap widens with the rate. At 5% the error is small enough to look like rounding. At 28% it is substantial, and on a large invoice it is the kind of mistake that gets noticed at audit.
The formulas
To add tax: Total = Base × (1 + rate/100)
To remove tax: Base = Total ÷ (1 + rate/100)
The tax component is then simply the difference between the two figures. The calculator shows both, so you can lift either onto an invoice.
Inclusive and exclusive pricing
Which direction you need depends on how prices are quoted in your market, and conventions differ sharply. Consumer prices in much of Europe, Australia and India are displayed tax-inclusive, so what you see on the shelf is what you pay. Prices in the United States are typically quoted exclusive of sales tax, which is added at the register.
In business-to-business trade, exclusive quoting is the norm almost everywhere, because registered businesses reclaim the tax and care about the net figure. If you are issuing an invoice, be explicit about which you have quoted — ambiguity here is a frequent source of disputes.
A note on rates
Most systems apply different rates to different categories of goods, often with essentials taxed at a reduced rate or exempted entirely. India uses a multi-slab structure. The EU sets national standard rates with reduced rates for specified categories. Pakistan applies a general sales tax with sector-specific variations.
The quick-pick buttons above cover common rates, but they are shortcuts rather than guidance. Check the rate applicable to your specific goods or services with your own tax authority, because getting the category wrong matters more than getting the arithmetic wrong.
Not tax advice. This calculator applies a rate you supply. It does not determine which rate applies to your transaction, handle reverse charge, input credits, exemptions, or cross-border rules. Consult a qualified tax professional for anything filed with an authority.
Frequently asked questions
How do I remove tax from a total?
Divide by one plus the rate as a decimal. For 18%, divide the gross figure by 1.18. Subtracting 18% from the total gives the wrong answer, because the percentage was calculated on the smaller base amount.
What is the difference between inclusive and exclusive?
An inclusive price already contains the tax; an exclusive price has it added at checkout or on the invoice. Consumer prices are commonly inclusive in Europe, Australia and India, and exclusive in the United States.
Why does subtracting the percentage give the wrong answer?
Because percentages are not reversible that way. Adding 18% then subtracting 18% does not return you to the start, since the second calculation is performed on a larger number than the first.
Which rate should I use?
Whichever applies to your specific goods or services under your jurisdiction's rules. Most systems have multiple rates by category, so check with your tax authority rather than assuming the standard rate.
Does this handle input tax credits?
No. This is a single-transaction calculator. Input credits, reverse charge, and reconciliation across a filing period are accounting operations that need proper software or an accountant.
Can I use this for VAT or sales tax?
Yes. GST, VAT and sales tax use identical arithmetic for a single transaction — only the rate and the rules about what it applies to differ.