GST Calculator

What is GST?

Goods and Services Tax is an indirect tax levied on the supply of goods and services in India. It replaced a layered patchwork of central and state taxes — excise duty, service tax, VAT, octroi, entry tax and others — with a single tax collected at each stage of the supply chain, from July 2017.

The defining feature is that GST is a value-added tax. A business charges GST on what it sells (output tax) and claims credit for the GST it paid on what it bought (input tax credit), remitting only the difference. The tax therefore accumulates on the value added at each stage rather than compounding on the full price at every hand-off — the "tax on tax" problem the old regime suffered from. Only the final consumer, who cannot claim credit, actually bears the cost.

Because India is a federation, a single tax has to be shared between the Union and the states. That is why one GST rate appears on invoices as two or three different components, which is the part that confuses most people and the part the transaction-type selector above handles.

What is a GST calculator?

A GST calculator does one narrowly defined job: it works out the tax portion of a price at a rate you supply. It answers two questions, and it is worth being precise about which is which, because they are not the same arithmetic.

The first is forward calculation: given a base price, how much tax is added and what is the final amount? This is what a seller needs to raise an invoice.

The second is reverse calculation: given a price that already includes tax, how much of it is tax and what was the price before? This is what a buyer needs to reconcile a receipt, what an accountant needs to book a purchase, and what anyone selling at a fixed MRP needs in order to know their actual revenue.

What a GST calculator does not do — and this matters — is decide which rate applies to your supply, determine the place of supply, work out whether a transaction is intra-state or inter-state, or establish whether you are liable to register or pay at all. Those are questions of classification and law. The calculator applies the rate you give it, correctly and to the paisa. Everything upstream of that is yours to determine.

How to calculate GST

Begin with the question that decides everything else: does the amount in front of me already include GST?

If it does not — a supplier quote, a base price, a contract value stated as "plus GST" — you are adding tax. Multiply by the rate and divide by 100, then add the result to the original amount.

If it does — an MRP, a shelf price, a restaurant bill, an all-inclusive quote — you are extracting tax. Divide by 1 plus the rate as a decimal, and the difference between the original amount and the result is the tax.

Everything else follows from those two operations. Splitting into CGST and SGST, applying IGST, adding a round-off line: all of it happens after the tax amount is known, and none of it changes the total.

How to add GST to an amount

The formula is GST = base × rate ÷ 100 and total = base + GST.

Say you are quoting consultancy work at ₹50,000 with GST at 18%. The tax is 50,000 × 18 ÷ 100 = ₹9,000, and the invoice total is ₹59,000. On an intra-state invoice that ₹9,000 appears as ₹4,500 CGST and ₹4,500 SGST; on an inter-state one it appears as ₹9,000 IGST. In all three cases your customer pays ₹59,000.

A useful shortcut for mental arithmetic: adding 18% means multiplying by 1.18, adding 12% means multiplying by 1.12, and adding 5% means multiplying by 1.05. Committing those three multipliers to memory covers the vast majority of everyday cases.

How to remove GST from an amount

The formula is base = inclusive ÷ (1 + rate ÷ 100) and GST = inclusive − base.

A customer pays ₹5,900 for a service inclusive of 18% GST. The base is 5,900 ÷ 1.18 = ₹5,000, and the tax inside is ₹900. Your revenue from that transaction is ₹5,000; the ₹900 was never yours — it is collected on behalf of the government and paid over.

This is the calculation people get wrong most often, and the error always takes the same shape: applying the rate directly to the inclusive figure. Eighteen percent of ₹5,900 is ₹1,062, which is ₹162 too high. The reason is straightforward once you see it — the ₹5,900 already contains the tax, so applying the rate again is charging tax on tax.

If you want a sanity check without a calculator, remember that a rate r applied forward becomes r ÷ (1 + r) when read backwards. Eighteen percent forward is 15.254% of the inclusive price. Twelve percent forward is 10.714%. Five percent forward is 4.762%. If your extracted tax is close to those proportions of the total, you have done it right.

How CGST and SGST are calculated

When the supplier and the recipient are in the same state or union territory, the supply is intra-state and the tax is shared between the Centre and the state. Central GST and State GST are each levied at half the total rate, on the same base.

At an 18% rate that means 9% CGST and 9% SGST. On a base of ₹10,000 the invoice shows ₹900 CGST and ₹900 SGST, and the customer pays ₹11,800. Both halves are calculated on the base amount, never on each other — SGST is not charged on top of CGST.

In a union territory without its own legislature, the state half is levied as UTGST instead of SGST. The arithmetic is identical and the calculator's intra-state mode covers both; only the label on the invoice line changes.

One detail worth understanding is what happens when the tax cannot be halved evenly. If the GST works out to ₹15.25, half is ₹7.625, and there is no such thing as half a paisa. Rounding both components to ₹7.63 gives ₹15.26 — a rupee-and-paise mismatch against the total, and an invoice that will not reconcile. This calculator rounds one half and derives the other by subtraction, so CGST shows ₹7.63, SGST shows ₹7.62, and the pair sums to exactly ₹15.25.

How IGST is calculated

When the supplier and the recipient are in different states, the supply is inter-state and Integrated GST applies instead of the CGST/SGST pair. IGST is levied at the full rate — 18% is 18% IGST, not two components of 9%.

On the same ₹10,000 base at 18%, an inter-state invoice shows a single IGST line of ₹1,800 and a total of ₹11,800. The customer pays exactly what they would have paid intra-state. What changes is not the amount but the mechanism: IGST is collected by the Centre and the destination state's share is settled between governments afterwards, which is what makes GST a destination-based tax without requiring the seller to register in every state they ship to.

IGST also applies to imports and to supplies to and from special economic zones. Determining whether a given transaction is intra-state or inter-state depends on the place of supply rules, which for services in particular are not simply "where the customer is". That determination is outside what any calculator can do for you.

GST rates in India

GST is levied through a small number of slabs rather than a single universal rate. The structure has historically centred on 5%, 12%, 18% and 28%, alongside a nil rate for exempt and zero-rated supplies and special rates such as 0.25% for rough diamonds and 3% for gold and precious metals.

That structure is not fixed. The GST Council revises rates and reclassifies items periodically, and there have been substantive rationalisations of the slab structure since 2017. Any list of "GST rates in India" published on a calculator page — including this one — is a snapshot, and the only reliable source for the rate applying to a specific supply on a specific date is official notification.

Two further complications are worth knowing about. First, certain goods attract compensation cess over and above GST — typically tobacco, aerated drinks, coal and larger motor vehicles. Cess is calculated separately, sometimes on a different basis entirely, and is not part of the GST rate. This calculator does not model it. Second, some supplies are exempt while others are zero-rated, and while both mean no tax is charged to the customer, they differ in whether input tax credit can be claimed — a distinction that matters a great deal to a business and not at all to the arithmetic.

How to calculate 5% GST

Multiply the base by 0.05, or equivalently divide by 20. On ₹10,000 the GST is ₹500 and the total is ₹10,500. Intra-state that splits into ₹250 CGST and ₹250 SGST.

To extract 5% GST from an inclusive price, divide by 1.05. A ₹1,050 inclusive amount contains ₹1,000 of base and ₹50 of tax. As a proportion, 5% GST is 4.762% of the tax-inclusive price.

How to calculate 12% GST

Multiply the base by 0.12. On ₹10,000 the GST is ₹1,200 and the total is ₹11,200, splitting into ₹600 CGST and ₹600 SGST intra-state.

To extract it, divide the inclusive amount by 1.12. ₹11,200 inclusive contains ₹10,000 base and ₹1,200 tax. Twelve percent GST is 10.714% of the inclusive price.

How to calculate 18% GST

Eighteen percent is the slab most people encounter, and multiplying by 0.18 gives the tax directly. On ₹10,000 that is ₹1,800 and a total of ₹11,800, splitting into ₹900 CGST and ₹900 SGST.

To extract 18% GST from a tax-inclusive price, divide by 1.18. ₹11,800 inclusive contains ₹10,000 base and ₹1,800 tax. Note again that this is 15.254% of the inclusive figure, not 18% — a distinction worth several hundred rupees on a mid-sized invoice.

A handy approximation for the reverse direction: the GST inside an 18% inclusive price is a little over one-seventh of it. On ₹11,800, one-seventh is about ₹1,686 against a true ₹1,800 — close enough to catch a serious error at a glance, though not close enough to put on an invoice.

How to calculate 28% GST

Multiply the base by 0.28. On ₹10,000 the GST is ₹2,800 and the total ₹12,800, splitting into ₹1,400 CGST and ₹1,400 SGST intra-state.

To extract it, divide by 1.28: a ₹12,800 inclusive amount contains ₹10,000 base and ₹2,800 tax. Twenty-eight percent GST is 21.875% of the inclusive price. Be particularly careful with this slab — many goods in it also attract compensation cess, so the total tax on the invoice may exceed what a 28% calculation alone suggests.

How to calculate GST from a tax-inclusive price

This is the reverse calculation, and it deserves its own treatment because of how frequently it comes up in practice. Retail prices in India are typically quoted inclusive of GST, so anyone selling at MRP, reconciling a card statement, or booking a purchase invoice is working backwards.

Switch the calculator to Remove GST, enter the total you actually paid or received, and select the rate. The base and the tax appear separately, and the two always sum to exactly the figure you entered — a property this tool guarantees rather than approximates.

The practical value shows up in margin calculations. If you sell an item at ₹1,180 inclusive of 18% GST, your revenue is ₹1,000, not ₹1,180. Treating the full ₹1,180 as revenue overstates your turnover by 18% and will produce a margin figure that is simply wrong. Every unit price you compare against a cost price needs to be on the same tax footing.

GST on ₹1,000

At 5% the GST is ₹50 and the total ₹1,050. At 12% it is ₹120 and ₹1,120. At 18% it is ₹180 and ₹1,180. At 28% it is ₹280 and ₹1,280.

Read the other way, a ₹1,000 price that already includes tax breaks down as ₹952.38 base plus ₹47.62 GST at 5%; ₹892.86 plus ₹107.14 at 12%; ₹847.46 plus ₹152.54 at 18%; and ₹781.25 plus ₹218.75 at 28%.

GST on ₹5,000

At 5% the GST is ₹250 and the total ₹5,250. At 12% it is ₹600 and ₹5,600. At 18% it is ₹900 and ₹5,900. At 28% it is ₹1,400 and ₹6,400.

Inclusive of 18% GST, ₹5,000 contains ₹4,237.29 of base and ₹762.71 of tax. Intra-state that tax splits into ₹381.36 CGST and ₹381.35 SGST — another odd-paisa case where the halves differ by one paisa so that they still sum correctly.

GST on ₹10,000

At 5% the GST is ₹500 and the total ₹10,500. At 12% it is ₹1,200 and ₹11,200. At 18% it is ₹1,800 and ₹11,800. At 28% it is ₹2,800 and ₹12,800.

Inclusive of 18% GST, ₹10,000 contains ₹8,474.58 of base and ₹1,525.42 of tax.

GST on ₹50,000

At 5% the GST is ₹2,500 and the total ₹52,500. At 12% it is ₹6,000 and ₹56,000. At 18% it is ₹9,000 and ₹59,000. At 28% it is ₹14,000 and ₹64,000.

Inclusive of 18% GST, ₹50,000 contains ₹42,372.88 of base and ₹7,627.12 of tax. At this size the round-off line starts to matter on real invoices — enable it in the display options to see the adjustment to the nearest rupee.

GST on ₹1 lakh

At 5% the GST is ₹5,000 and the total ₹1,05,000. At 12% it is ₹12,000 and ₹1,12,000. At 18% it is ₹18,000 and ₹1,18,000. At 28% it is ₹28,000 and ₹1,28,000.

Inclusive of 18% GST, ₹1,00,000 contains ₹84,745.76 of base and ₹15,254.24 of tax. Note the Indian digit grouping throughout — ₹1,18,000 rather than ₹118,000 — which this calculator uses everywhere because it is what Indian invoices and accounting software expect.

Common GST calculation mistakes

Applying the rate to a tax-inclusive amount. The single most common error, covered above. Eighteen percent of an inclusive figure overstates the tax by about 18% of itself.

Charging SGST on top of CGST. Both are calculated on the base amount independently. They are not sequential and the second is not applied to a base that includes the first.

Adding CGST, SGST and IGST together. A transaction is either intra-state or inter-state, never both. An invoice showing all three lines for the same supply is wrong.

Rounding each line independently. Round the tax and derive the total, or round the base and derive the tax — but do not round all three separately and hope they agree. They frequently will not, and the mismatch surfaces later in reconciliation.

Assuming a rate from a product category. Classification is genuinely difficult, rates change, and similar-sounding items can sit in different slabs. Look the rate up rather than inferring it.

Forgetting compensation cess. On goods that attract it, the GST calculation alone understates the total tax on the invoice.

Treating gross receipts as revenue. The tax component of an inclusive price was never income. Booking it as revenue inflates turnover and distorts every margin derived from it.

Using a GST calculator for business

For a registered business the daily uses cluster into a few patterns. Quoting: take an agreed base price and produce the tax-inclusive figure the customer will actually be billed. Purchase reconciliation: take a supplier's inclusive total and separate out the input tax credit you can claim. Pricing: work backwards from a target shelf price to the base price that leaves the margin you need.

That last one is worth spelling out. If you want to sell at a round ₹999 inclusive of 18% GST, your base price is ₹846.61 and the tax is ₹152.39. If your landed cost is ₹700, your margin is ₹146.61 on a base of ₹846.61 — about 17.3%. Computing that margin against the ₹999 sticker instead would suggest 29.9%, which is not a small error to build a business on.

Using a GST calculator for invoices

A compliant tax invoice shows the taxable value, the rate, and the tax split into its components, with the total. The calculator's Copy button produces exactly that structure as text, ready to paste into an invoice template or an email.

Two invoice conventions are worth matching. First, the tax split must reconcile — CGST plus SGST equals the total GST, exactly, which the calculator guarantees. Second, invoice totals are commonly rounded to the nearest rupee with the adjustment shown on a separate round-off line rather than silently absorbed; enable that option and the calculator shows both the adjustment and the rounded payable amount.

What the calculator does not produce is an invoice. It has no notion of GSTIN, HSN or SAC codes, place of supply, invoice numbering or reverse charge. It computes the tax lines; your accounting or billing software handles the document.

Using a GST calculator as a buyer

As a consumer the useful question is usually how much of what you paid was tax. Enter the bill total, switch to Remove GST, pick the rate on the invoice, and the split appears. It is a quick way to sanity-check a bill — if a restaurant charges you tax on a figure that already looked tax-inclusive, or applies a rate that does not match the one printed, the arithmetic will show it.

For a registered business buying inputs, the same calculation identifies the input tax credit available on a purchase, provided the supplier's invoice is valid and the purchase is eligible. Whether it is eligible is a question of law, not arithmetic.

Using a GST calculator as a seller

Sellers work in both directions constantly. Forward, to turn an agreed price into an invoice total. Backwards, to work out what a fixed-price sale actually contributes once the tax collected is set aside.

The habit worth building is to keep base prices and inclusive prices clearly separated everywhere in your records — in your catalogue, your quotes, your margin sheets. Most GST confusion inside small businesses traces back to a single spreadsheet column where the two got mixed together and nobody could later tell which was which.

How this calculator handles rounding

Rounding sounds like a display concern and is not. If base, tax and total are each computed and rounded independently, they will sometimes disagree by a paisa, and an invoice whose lines do not add up to its own total is a real problem.

This calculator avoids the issue structurally. All arithmetic is performed in integer paise rather than decimal fractions, so results never drift into floating-point artifacts such as 1800.0000000002. Within any breakdown, exactly one figure is obtained by subtraction rather than by its own formula: when adding GST, the total is the sum of base and tax; when removing it, the tax is the difference between total and base. The figure you typed is never altered. The result is that the components always reconcile exactly, which the calculator confirms beneath each breakdown.

The same principle governs the CGST and SGST split, where one half is rounded and the other derived, so the pair always sums to the tax even when the tax is an odd number of paise.

Privacy

Every calculation on this page runs in your browser. There is no server involved, no request made and nothing transmitted — the amounts you enter never leave your device. That is worth stating plainly for a tool where people type real invoice values, contract amounts and turnover figures.

Nothing is stored either, unless you ask for it. The optional calculation history writes to your own browser's local storage and only when you switch it on; turning it off deletes the entries immediately. Shareable links are created only when you press the button, so amounts are never written into the address bar — and therefore never into browser history or a Referer header — as a side effect of typing.