Add or remove GST at 5%, 12%, 18%, or 28% — with the full tax breakup, CGST/SGST split, and reverse calculation in one click.
India’s Goods and Services Tax replaced a thicket of central and state taxes in 2017 — but doing the arithmetic by hand still trips people up, especially the reverse calculation: given a GST-inclusive price, what was the original price and how much of it is tax? Our free GST Calculator handles both directions at all four standard slabs — 5%, 12%, 18%, and 28% — and shows the full breakup including the CGST/SGST split used on Indian invoices.
The two modes answer the two questions businesses and shoppers actually ask. Add GST: a supplier quotes a base price of 1,000 and you need the invoice total — at 18%, GST is 180 and the total is 1,180. Remove GST: a customer paid 1,180 inclusive of 18% GST and you need to know the taxable value for your books — the base is 1,180 divided by 1.18, which is 1,000.00, and the GST embedded is 180.00. The reverse formula is the one people get wrong (it is not 18% of 1,180), which is why the widget exists.
Beyond India, the same math answers VAT questions across Europe, the UK, and the Gulf, and sales-tax questions in the US — a 20% VAT added to a 100 price is the same calculation as 18% GST on 1,000, with different numbers. The mechanics of inclusive versus exclusive tax are universal; only the slab names change. Use the calculator for invoicing, for checking restaurant bills, for reconciling purchase orders, or for settling the eternal argument about how much of the price was “actually tax.”
GST is a destination-based tax on the supply of goods and services — “destination-based” meaning the tax belongs to the state where the goods are consumed, not where they are made. On an intra-state sale (buyer and seller in the same state), the GST splits into two equal halves: CGST (Central GST, going to the central government) and SGST (State GST, going to the state). An 18% GST invoice therefore shows 9% CGST + 9% SGST — the widget displays this split automatically, matching the format Indian invoices require.
On inter-state sales, the two halves merge into IGST (Integrated GST) at the full slab rate, collected by the center and apportioned to the destination state. The calculator’s GST figure is the IGST figure for inter-state transactions — same number, different label. Imports and e-commerce supplies work the same way: one rate, one tax amount, with the label depending on the transaction’s geography.
The four slabs reflect policy choices: 5% for essentials and mass-consumption goods, 12% for standard goods, 18% for most services and the default business slab, and 28% for luxury and sin goods (plus compensation cess on items like tobacco and automobiles). Some items are exempt (0%) or taxed at 0.25%/3% (precious metals) — outside this calculator’s four slabs, but the same formulas apply with any rate.
Key terms:
The Remove formula is the critical one: dividing by 1.18 unwraps the tax correctly, while the common mistake — taking 18% of 1,180 (212.40) — overstates the tax by nearly 40%. Whenever a price “includes GST,” divide, do not multiply.
A freelance designer quotes 25,000 for a project. Design services fall under the 18% slab. She needs the invoice total.
Had she quoted “25,000 inclusive,” her real revenue would be 25,000 ÷ 1.18 = 21,186.44 — a 3,813.56 haircut she never intended. The Add/Remove distinction is worth real money.
A restaurant bill totals 1,000 and the menu says prices are inclusive of GST at 18%. How much was the food, and how much was tax?
Note that restaurants actually charge 5% GST without input tax credit — at 5%, a 1,180 bill unwraps to 1,123.81 base and 56.19 tax. Always confirm the applicable slab before reverse-calculating.
A boutique owner closes the month with 4,80,000 in GST-inclusive sales, mostly apparel at 12%. For her GST return she needs taxable value and tax collected: 4,80,000 ÷ 1.12 = 4,28,571.43 taxable value; tax = 51,428.57 (CGST 25,714.29 + SGST 25,714.29). Against this she claims input tax credit of 38,000 paid on inventory purchases — net GST payable: 13,428.57. The calculator’s Remove mode produced the first two numbers in seconds; the ITC subtraction is the return’s logic. Doing this by hand across mixed slabs (some items at 5%, some at 12%) is where businesses hire accountants — but understanding the per-slab math is what lets her check the accountant’s work.
Second scenario: an exporter quotes a foreign buyer. Exports are zero-rated under GST — 0% — so the quote is simply the base price with no tax added, and the exporter claims a refund of the input tax credit accumulated on inputs. A buyer comparing a domestic quote (base + 18%) against an export quote must use Add mode for one and no-tax for the other; mixing them up is a classic RFQ error that this calculator prevents by making the mode explicit.
India’s GST (2017): subsumed excise duty, service tax, VAT, octroi, and a dozen cesses into one tax — the “one nation, one tax” reform. The dual CGST/SGST structure preserves fiscal federalism: both center and states tax the same base simultaneously. E-invoicing and monthly returns (GSTR-1, GSTR-3B) digitized compliance, and input tax credit flowing through the chain is what killed the old cascading “tax on tax” effect.
VAT equivalence: the UK’s 20% VAT, the EU’s 19–27% national VATs, and the Gulf’s 5% VAT are mechanically identical to GST — a value-added tax collected at each stage with input credits. This calculator’s Add/Remove math works for all of them: enter the VAT rate as the “GST rate” and the arithmetic is the same. A London freelancer adding 20% VAT to a 1,000 quote gets 1,200 by the identical formula.
US sales tax: American sales tax is simpler in arithmetic (a single rate added at the final sale, no input credits, typically 0–10%+) but messier in practice — thousands of overlapping state, county, and city jurisdictions, each with its own rate and rules. The Add mode handles any of them: enter the combined rate and go. There is no American equivalent of Remove mode in daily life, because US shelf prices are quoted exclusive of tax by law and custom.
Why slabs differ: essentials at 5%, luxuries at 28% — the slab structure is fiscal policy expressed as arithmetic. When governments move items between slabs (as India has done repeatedly since 2017), every business reprices using exactly these two formulas. The calculator does not need updating when slabs change; only the rate input does.
Composition scheme: small Indian businesses (turnover under 1.5 crore for goods) can opt for a flat 1% composition levy instead of regular GST — simpler, but no input tax credit and no tax charged to customers. The regular Add/Remove math does not apply to them, which is itself a useful thing for a small trader to verify before opting in.
Zero-rating vs. exemption: exports are zero-rated (0% GST with input tax credit refunds); exempt goods (fresh food, healthcare) are 0% without credit refunds — the supplier absorbs the input tax. The invoice arithmetic looks identical (no tax added); the business economics differ enormously.
One pattern worth internalizing: inclusive versus exclusive is a convention, not a math problem. B2B India quotes exclusive (the buyer claims ITC, so the tax is pass-through); B2C India quotes inclusive (the consumer cannot claim credit, so the all-in price is what matters); the US quotes exclusive everywhere; Europe quotes inclusive everywhere. Know your market’s convention, pick the matching mode, and the arithmetic takes care of itself.
A brief history of the tax this calculator computes: France invented the value-added tax in 1954 (Maurice Lauré, a tax official, designed it to replace cascading production taxes), and the idea spread to 170+ countries because it solves the oldest problem in sales taxation — tax pyramiding, where tax-on-tax compounds through a supply chain. India’s journey was longer: a 2000 empowered committee, the 2011 constitutional amendment bill lapsing, the 2016 101st Amendment finally enabling it, and the midnight launch of July 1, 2017 merging 17 taxes and 23 cesses. Early GST had the infamous four slabs plus cess and glitchy portal filings; a decade of rate rationalization has simplified but not eliminated the slab structure. Every one of those reforms changed rates, never the underlying divide-or-multiply arithmetic — which is why a calculator built on the two formulas stays correct through every policy cycle.
Worked scenario — the mixed-slab invoice: a hotel bill shows room charges 8,000 (18% slab for rooms over 7,500), food 2,000 (5% restaurant rate), and laundry 500 (18% services). Compute per line: room GST 1,440, food GST 100, laundry GST 90 — total GST 1,630, invoice total 12,130. A single blended rate would be wrong on every line; GST is always computed per line item at its own slab, then summed. Businesses that average slabs across an invoice file incorrect returns — the calculator’s one-rate-at-a-time design enforces the correct habit: run it per line, add the results.
Edge cases and pro tips: precious metals sit at 3% and rough diamonds at 0.25% — outside the widget’s four slabs, but the formulas accept any rate, so compute manually with the same steps. MRP-inclusive pricing (mandatory on packaged goods in India) means the shelf price already contains GST — use Remove mode to find the taxable value. Discounts and coupons: GST applies to the transaction value after discounts, so always subtract discounts before adding tax. And the pro move for businesses: reconcile the calculator’s per-invoice GST against your GSTR-1 filing monthly — a persistent gap means a slab misclassification somewhere, and finding it before the tax department does is worth far more than the arithmetic.
When this calculator is not enough: this widget nails the arithmetic, but GST compliance also involves HSN/SAC classification (which slab applies), place-of-supply rules (CGST+SGST vs. IGST), input tax credit reconciliation (GSTR-2B matching), reverse-charge entries, and filing deadlines. Use the calculator for every invoice line and return figure; use a CA or GST software for classification and filing. Correct arithmetic on the wrong slab is still a wrong return — the calculator guarantees the math, you guarantee the slab.
GST calculator: Add mode GST = base x rate/100, total = base + GST; Remove mode base = inclusive/(1+rate/100), GST = inclusive – base; CGST = SGST = GST/2 intra-state. Default example: 1000 at 18% add yields GST 180 (CGST 90 + SGST 90), total 1180; remove from 1000 yields base 847.46, GST 152.54. Same arithmetic as VAT and sales tax. Source: Sigma Calculator, GST Calculator, https://sigmacalculator.net/e-commerce-calculators/gst-calculator/
Cite this page as: GST Calculator, Sigma Calculator, https://sigmacalculator.net/e-commerce-calculators/gst-calculator/
Last updated: October 12, 2026