GST is a percentage added on top of the taxable value — 18% is the most common rate for services in India. The question is which number the customer sees. An exclusive price is the taxable value with GST added at checkout: the tag says ₹1,000 and you pay ₹1,180. An inclusive price already contains the tax: the tag says ₹1,180 and the taxable value hidden inside is ₹1,000.
The math both ways
- Exclusive → total: taxable value × (1 + rate/100). ₹1,000 at 18% → ₹1,180. The GST shown on the invoice is ₹180.
- Inclusive → taxable value: total ÷ (1 + rate/100). ₹1,180 at 18% → ₹1,000 taxable, ₹180 GST. Note that you divide, not subtract 18% — subtracting would give ₹967.60, which is wrong.
- Reverse calculation: if you know the total and want the tax, it's total − total ÷ (1 + rate/100).
The divide-don't-subtract trap
Because 18% of ₹1,000 is ₹180, some people assume an inclusive ₹1,180 contains ₹212.40 of tax (18% of 1,180). It doesn't — the tax is always a percentage of the taxable value, not of the tax-inclusive total.
Which to use where
In retail, prices are usually shown inclusive because that's the amount the customer pays. In B2B quotations, exclusive pricing is common because the buyer wants to see the taxable value and claim input credit. What matters legally is that your invoice states both the taxable value and the GST separately — the invoice is the document that gets audited, and mixing up inclusive and exclusive is one of the most common small-business GST errors.
A quick conversion example
You want to sell a service for ₹5,000 before GST at 18%. Your invoice shows: taxable value ₹5,000, CGST ₹450, SGST ₹450, total ₹5,900. A competitor advertises the same service at ₹5,900 inclusive — same bottom line, but now you can see their taxable value was ₹5,000 too. Never compare a GST-exclusive quote with a GST-inclusive price without converting.
Calculate GST either way
ForgePlug's GST Calculator handles inclusive, exclusive, and reverse calculations, splits CGST/SGST/IGST, and even builds a full multi-line invoice breakdown.
Open GST CalculatorWhy the same 18% splits differently
The total rate does not change, but how it is divided depends on where the supply goes. For a transaction within one state, the 18% is split into two equal halves — 9% CGST to the centre and 9% SGST to the state — which is why the worked example above shows ₹450 and ₹450 rather than a single ₹900 line. For a transaction across state lines, the same 18% is charged as a single IGST line of ₹900.
Getting this wrong is one of the more common invoicing errors, and it is not cosmetic: the split determines which government receives the money, so a mislabelled invoice creates a reconciliation problem for both parties. What decides it is the place of supply rather than where your office happens to be, and for services delivered remotely that is usually the recipient's registered location.
Input tax credit — the reason B2B quotes exclusive
A registered business does not ultimately bear the GST it pays on its own purchases. It claims that amount back as input tax credit and offsets it against the GST it collects from its customers. Only the difference is paid to the government, which is what makes GST a tax on value added rather than a tax charged repeatedly along a supply chain.
This is exactly why a business buyer wants to see the exclusive figure. To them the tax is recoverable, so the taxable value is the real cost and the GST line is a pass-through. A retail consumer cannot reclaim anything, so the inclusive total is the only number that means anything to them. The two audiences are not being shown different prices — they are being shown the number that is actually relevant to each.
That credit depends on the paperwork being right. A buyer generally cannot claim credit against an invoice missing the supplier's GSTIN, the correct HSN or SAC code, or a proper tax breakup — which turns an invoicing shortcut into a direct cost for your customer, and a fast way to be chased for a corrected document.
Composition scheme businesses work differently
Small businesses registered under the composition scheme pay a flat rate on turnover and cannot charge GST separately on their invoices or pass on input tax credit. If a supplier's invoice shows no GST breakup, check whether they are a composition dealer before assuming the invoice is incorrect.
Rounding, and where the paise go
Inclusive-to-exclusive conversion rarely divides cleanly. An inclusive price of ₹1,000 at 18% gives a taxable value of ₹847.4576…, and the fraction has to land somewhere. Round each line item rather than only the invoice total, and be consistent about it — the usual convention is to round the tax amount to two decimals per line and let the invoice total follow from the rounded lines.
The reason to be careful is that your customer's accounting system will recompute these figures independently. If their arithmetic produces a total a rupee away from yours, the invoice can be queried or rejected outright, and a one-rupee discrepancy takes the same amount of time to resolve as a large one. Setting round inclusive prices for retail — and round exclusive prices for B2B — avoids most of it.