GST & VAT Calculator
Add tax to a price, or pull it back out of a total that already includes it. The second direction is division, not subtraction, and this is where most manual calculations go wrong.
1000 × 18% = 180 tax, so the total is 1180Calculated in your browser. Invoice figures are never sent anywhere or stored.
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How to use the tax calculator
- Choose a direction. Either you have an amount before tax and want the total, or you have a total that already includes tax and want it broken out.
- Enter the amount and the tax rate. Preset buttons cover the common rates for several countries.
- Read the three figures — net, tax and gross — along with the working that produced them.
- Check the split bar for a quick visual sense of how much of the total is tax.
Nothing is uploaded. The calculation happens in your browser.
The mistake this tool exists to prevent
Adding tax is easy and almost nobody gets it wrong. Multiply by the rate, add the result.
Removing tax is where things go wrong, constantly, in real bookkeeping. The instinct is to subtract the percentage — and that instinct is wrong every single time.
Take a ₹1,180 total that includes 18% GST.
The wrong way: 1,180 − 18% = 1,180 − 212.40 = ₹967.60
The right way: 1,180 ÷ 1.18 = ₹1,000, with ₹180 of tax.
The gap is ₹32.40, and the wrong answer is not merely imprecise — it is internally inconsistent. Check it: 18% of ₹967.60 is ₹174.17, which added back gives ₹1,141.77, not the ₹1,180 you started with. The figure fails its own test.
The correct answer passes: 18% of ₹1,000 is ₹180, and ₹1,000 plus ₹180 is exactly ₹1,180.
Why division is the right operation
Because the tax was never calculated on the total.
When a seller adds 18% GST, they take the net price, multiply it by 0.18, and add the result. In one step: net × 1.18 = gross.
To reverse a multiplication you divide. Gross ÷ 1.18 = net. Nothing else undoes it.
Subtracting 18% from the gross applies the percentage to the wrong base — a larger number — so it removes too much. The size of the error scales with the rate. At 5% it is small enough to pass as a rounding difference; at 20% it is 3.3% of the total; at 28% it is over 6%, which on a year of invoices is not a rounding difference, it is a misstatement.
The calculator shows the division in the working every time you extract tax, and spells out what the subtraction would have given, so the difference is visible rather than assumed.
The VAT fraction, for mental arithmetic
UK bookkeeping has a shortcut worth knowing, and it generalises to any rate.
To find the tax inside a gross figure, multiply by rate ÷ (100 + rate). At 20% that is 20/120, which simplifies to one sixth. So the VAT in a £120 total is £120 ÷ 6 = £20 — no calculator required.
| Rate | Fraction of the gross that is tax |
|---|---|
| 5% | 1/21 |
| 10% | 1/11 |
| 15% | 3/23 |
| 18% | 9/59 |
| 20% | 1/6 |
| 25% | 1/5 |
| 28% | 7/32 |
The 10% and 20% cases are the ones worth memorising: divide by 11 for Australian GST, divide by 6 for UK VAT. Both give exactly the same answer as dividing the gross by 1.1 or 1.2 and subtracting.
What GST and VAT actually are
Both are consumption taxes collected in stages, and the staging is what distinguishes them from a simple retail sales tax.
A manufacturer sells components to a factory and charges tax. The factory reclaims that tax as an input credit, builds the product, sells it to a retailer and charges tax on the higher price. The retailer reclaims theirs, sells to a consumer and charges tax on the final price. At each stage the business pays over only the tax on the value it added, because it recovers what it paid upstream.
The consumer is the only party who cannot reclaim, so the whole burden lands there — but the revenue arrives in instalments throughout the chain rather than all at the final sale. That design makes evasion harder, because each business has a paper trail its suppliers also filed.
It also explains a practical difference in how prices are displayed. In countries with VAT or GST, consumer prices are usually quoted inclusive of tax, because everyone in the chain is dealing in tax-inclusive amounts anyway. In the United States, where tax is added only at the final sale and varies by locality, shelf prices are typically quoted exclusive, with tax appearing at the till.
Common rates around the world
India — GST. Slabs of 0%, 5%, 12%, 18% and 28%, with 18% the most common. Intra-state supplies split into CGST and SGST; inter-state supplies use a single IGST at the full rate.
United Kingdom — VAT. Standard 20%, reduced 5% for domestic energy and some other categories, zero on most food, children's clothing and books.
European Union. Member states set their own rates above an EU-mandated minimum standard rate of 15%. Common standard rates are 19%, 20%, 21%, 23% and 25%.
Australia — GST. A flat 10% on most goods and services, with basic food, health and education exempt.
New Zealand — GST. 15%, applied unusually broadly with very few exemptions.
Singapore — GST. 9%.
Canada. Federal GST of 5%, combined with provincial tax in several provinces as a single HST of 13% or 15%.
Rates change. Treat the presets here as a convenience, not as tax advice, and confirm the current figure with the relevant authority before it goes on an invoice.
Limits and requirements
One rate at a time. Composite charges — a federal rate plus a local one — need to be entered as their combined percentage.
No rate lookup. The tool does not determine which rate applies to your product or your customer's location. That is a legal question, not an arithmetic one.
Rounded to two decimal places. Matches standard invoice practice, but confirm your jurisdiction's rounding rule if you are producing formal documents.
Not tax advice. Registration thresholds, reverse charge, exemptions, place-of-supply rules and input credit restrictions all sit outside a calculator.
Privacy: how this tool handles your figures
Everything runs in your browser. Amounts, rates and results are never transmitted, logged or stored, and closing the tab discards them.
Invoice figures are commercially sensitive in a quiet, cumulative way. A single number reveals little; a session of them reveals your pricing, your margins and the size of your deals. Server-side calculators receive all of that, and request bodies routinely end up in access logs and error trackers that nobody set out to build as a business intelligence archive but which serve as one.
Multiplying by 1.18 does not require a server. You can verify that this one does not use one: open developer tools, watch the Network tab as you type, or disconnect from the internet after the page has loaded. The calculator carries on working.
Frequently asked questions
How do I remove GST or VAT from a total?
Divide, do not subtract. To take 18% GST out of a ₹1,180 total, divide by 1.18 to get ₹1,000 net, leaving ₹180 of tax. Subtracting 18% from ₹1,180 gives ₹967.60, which is wrong by more than ₹32. The reason is that the tax was calculated as a percentage of the smaller net figure, not of the total — so reversing it means undoing a multiplication, and the inverse of multiplying by 1.18 is dividing by 1.18.
Why does subtracting the percentage give the wrong answer?
Because a percentage is always a percentage of something, and adding and removing use different bases. When tax is added, 18% of the net is calculated and appended. When you subtract 18% from the gross, you are taking 18% of a larger number, so you remove too much. The error grows with the rate: at 5% it is small enough to look like a rounding difference, at 28% it is large enough to fail an audit.
What is the VAT fraction?
A shortcut used in UK bookkeeping for pulling tax straight out of a gross figure. At the 20% standard rate the fraction is one sixth, so the VAT in a £120 total is £120 divided by 6, which is £20. At the 5% reduced rate it is one twenty-first. The fraction is derived as rate divided by (100 plus rate) — 20/120 simplifies to 1/6. It gives exactly the same answer as dividing by 1.2 and subtracting; it is just easier to do in your head at the till.
What are the current GST rates in India?
The main slabs are 0%, 5%, 12%, 18% and 28%, with 18% covering the largest share of goods and services. Some categories carry an additional compensation cess on top, and rates are revised periodically by the GST Council. For an intra-state supply the total splits evenly into CGST and SGST — an 18% charge is 9% each — while an inter-state supply is levied as a single IGST at the full rate. The split does not change the total, so the figures here apply either way.
Is this the same as sales tax in the United States?
No, and the difference matters for how prices are displayed. GST and VAT are collected at every stage of production, with businesses reclaiming what they paid on their inputs, so the tax lands on the final consumer once. US sales tax is levied only at the final retail sale, and rates are set at state, county and city level, so a single transaction can combine several. This calculator handles the arithmetic of any single combined rate, but it will not look up a US rate for you — those depend on the exact delivery address.
Should I calculate tax per line item or on the invoice total?
Per line item is the safer default, because different products often attract different rates and most tax authorities expect the breakdown shown that way. Rounding each line separately and rounding the invoice total can differ by a cent or two, and jurisdictions vary on which they require. If your invoices are ever going to be audited, follow the local rule rather than whichever is more convenient — and use accounting software that applies it consistently.
Can I reclaim the tax I pay on business purchases?
Usually yes, if you are registered for GST or VAT. Tax paid on business inputs is generally recoverable as an input tax credit, offset against the tax you collect on sales, with the difference paid to or refunded by the authority. The rules have real exceptions — entertainment, some vehicles and anything used privately are commonly blocked or restricted — and you need a valid tax invoice for every claim. Check the specifics with an accountant for your jurisdiction.
Are my invoice figures sent anywhere?
No. The calculation happens in your browser and nothing is transmitted, logged or stored. Closing the tab discards it. Invoice amounts, margins and client totals are commercially sensitive, and there is no reason for a multiplication to require a server.