Short answer
To add GST: GST = Base × Rate ÷ 100, then Total = Base + GST. On ₹10,000 at 18%, GST is ₹1,800 and the total is ₹11,800.
To remove GST: Base = Total × 100 ÷ (100 + Rate). On ₹11,800 inclusive of 18%, the base is ₹10,000 and GST is ₹1,800.
On an intra-state supply the GST splits equally into CGST and SGST — 9% each at an 18% rate. On an inter-state supply the full 18% is charged as IGST instead.
How to use this GST calculator
- Choose add or removePick Add GST when the price you have excludes tax, or Remove GST when the figure already includes it.
- Enter the amountType it in, or tap a preset such as ₹10,000. The result updates as you type — there is no calculate button to press.
- Select the GST rateChoose the slab that applies to your goods or services. If you are unsure, that is a classification question, not a maths question — see the note below the rate table.
- Choose the transaction typeIntra-state splits the tax into CGST and SGST. Inter-state charges a single IGST at the full rate.
- Read and copy the resultBase, GST, total and the tax split appear immediately. Copy for invoice puts the full breakdown on your clipboard for pasting into your billing software.
What is GST?
Goods and Services Tax is a comprehensive indirect tax on the supply of goods and services across India. It came into force on 1 July 2017, replacing VAT, service tax, central excise duty and a range of other central and state levies.
GST works on a “one nation, one tax” principle: the same rate applies to a given product or service regardless of the state it is supplied in. It removed the cascading effect of the earlier system, where tax was charged on tax at each stage of the supply chain.
Key characteristics
- A single indirect tax. GST replaced more than a dozen central and state taxes with one framework.
- Destination-based. Tax accrues to the state where goods or services are consumed, not where they are produced.
- Input tax credit throughout. Registered businesses claim credit for GST paid on purchases, so tax is borne only on value added.
- Digital compliance. Returns are filed through the GSTN portal, with invoice-level reporting feeding your customers’ credit.
- Rate assigned by classification. Slabs attach to HSN codes for goods and SAC codes for services, not to broad categories.
How GST works through a supply chain
GST is charged at every stage, but input tax credit means each party pays tax only on the value it adds. The final burden sits with the end consumer. Take a product moving through three hands at 18%:
| Party | Sale price | GST @ 18% | ITC claimed | Net to government |
|---|---|---|---|---|
| Manufacturer | ₹1,000 | ₹180 | — | ₹180 |
| Wholesaler | ₹1,500 | ₹270 | ₹180 | ₹90 |
| Retailer | ₹2,000 | ₹360 | ₹270 | ₹90 |
The government collects ₹360 in total — exactly 18% of the final ₹2,000 price. Each business in the chain has paid tax only on its own margin. This is the mechanism that distinguishes GST from the pre-2017 system, where each stage taxed the full value including tax already paid.
Current GST slabs in India
The slab structure changed materially in the September 2025 reform. The 12% and 28% slabs were withdrawn, most 12% items moved to 5%, most 28% items moved to 18%, and a new 40% rate was introduced for luxury and demerit goods.
| Rate | GST on ₹10,000 | Typically applies to |
|---|---|---|
| 0% | ₹0 · total ₹10,000 | Fresh unprocessed essentials, and a range of items moved to nil in the 2025 reform |
| 0.25% | ₹25 · total ₹10,025 | Rough diamonds and unprocessed precious stones |
| 3% | ₹300 · total ₹10,300 | Gold, silver and jewellery |
| 5% | ₹500 · total ₹10,500 | Essentials and most items formerly taxed at 12% |
| 18% | ₹1,800 · total ₹11,800 | The standard rate — most services and consumer goods, including much of what previously sat at 28% |
| 40% | ₹4,000 · total ₹14,000 | Luxury and demerit goods |
Rates attach to HSN codes for goods and SAC codes for services, not to broad categories. Two products that look similar can sit in different slabs, and tobacco products were treated separately during the transition. Where a classification is genuinely arguable, get a written position rather than relying on a rate table.
Rate schedules notified under the CGST and IGST Acts, revised with effect from 22 September 2025Alcohol for human consumption and petroleum products remain outside GST and are taxed separately by state governments.
CGST, SGST, IGST and UTGST
The rate is the same either way. What changes is who collects it and how it appears on the invoice.
- CGST — the Centre’s share of an intra-state supply. At 18%, that is 9%.
- SGST — the state’s share of the same intra-state supply, at an equal rate.
- IGST — a single levy at the full rate on inter-state supplies and on imports, collected by the Centre and apportioned to the destination state.
- UTGST — takes the place of SGST in Union Territories without a legislature, such as Chandigarh and Lakshadweep.
Applying the wrong pair is a common invoicing error. It rarely changes what you collect, but it does break your customer’s input tax credit reconciliation — which is how it usually gets discovered.
The GST calculation formula
Adding GST to a base price
Use this when the quoted price excludes tax.
GST = (Base price × Rate) ÷ 100Total = Base price + GST
Example. Software services worth ₹50,000 at 18%. GST is (50,000 × 18) ÷ 100 = ₹9,000, so the invoice total is ₹59,000. On an intra-state supply that shows as ₹4,500 CGST and ₹4,500 SGST.
Removing GST from an inclusive price (reverse GST)
Use this when the figure you have already contains the tax.
Base = Total × 100 ÷ (100 + Rate)GST = Total − Base
Example. A price of ₹59,000 inclusive of 18%. Base is 59,000 × (100 ÷ 118) = ₹50,000, so the GST component is ₹9,000.
Finding the rate from two figures
If you know both the base and the total and want to check which slab was applied: Rate = ((Total − Base) ÷ Base) × 100. Useful for auditing vendor invoices and spotting a wrongly applied slab before you claim credit on it.
Do you need GST registration?
Registration becomes compulsory once aggregate turnover crosses the threshold in section 22 of the CGST Act — broadly ₹40 lakh for goods and ₹20 lakh for services, with lower thresholds of ₹20 lakh and ₹10 lakh in special category states. Section 24 lists categories that must register regardless of turnover, including persons liable to pay tax under reverse charge, casual and non-resident taxable persons, and those supplying through an e-commerce operator required to collect tax at source.
A point widely reported incorrectly: inter-state supply of services does not by itself force registration. Inter-state service suppliers are exempt from compulsory registration up to the aggregate turnover threshold. The rule people are thinking of applies mainly to goods.
CGST Act 2017, ss. 22 and 24; Notification 10/2017-Integrated Tax dated 13 October 2017Many businesses below the threshold register voluntarily, either to claim input tax credit on their own purchases or because corporate customers will not onboard a vendor without a GSTIN. If you invoice clients abroad, registration is also the gateway to exporting under a Letter of Undertaking without paying IGST.
Setting up a new business? See GST registration, or start with choosing a business structure.
Where this calculator gets used
- Raising invoices — getting the GST line and the CGST/SGST split right first time.
- Checking vendor bills — confirming the correct slab was applied before you claim credit on it.
- Quoting — converting between inclusive and exclusive pricing when a client asks for “all-in”.
- Marketplace payouts — reconciling what a platform deducted against what you expected.
Frequently asked questions
What is a GST calculator?
A free online tool that works out GST on any amount. It adds GST to a base price, removes GST from an inclusive price, and splits the tax into CGST and SGST for intra-state supplies or IGST for inter-state supplies.
What are the current GST slabs in India?
0%, 5%, 18% and 40%, following the reform effective 22 September 2025, plus special rates of 3% for gold and jewellery and 0.25% for rough diamonds. The 12% and 28% slabs were withdrawn, with most 12% items moving to 5% and most 28% items moving to 18%.
How do you calculate GST manually?
To add GST, multiply the base by the rate and divide by 100, then add it back. To remove GST, divide the inclusive amount by (100 + rate) and multiply by 100 to get the base.
How do you add GST to a price?
GST equals base × rate ÷ 100. On ₹50,000 at 18%, GST is ₹9,000 and the final price is ₹59,000.
How do you remove GST from a total amount?
Divide the inclusive amount by (100 + rate) and multiply by 100. ₹59,000 inclusive of 18% gives a base of ₹50,000, so GST is ₹9,000.
What is a GST-inclusive price?
A price that already contains the tax. The quoted figure is what the buyer pays in total, and the GST component has to be extracted for invoicing and input tax credit purposes.
What is a GST-exclusive price?
A base value before tax, with GST added on top. Business-to-business quotes are commonly given exclusive of GST.
When is GST split into CGST and SGST?
On intra-state supplies, where supplier and place of supply are in the same state. GST splits equally — 9% and 9% at an 18% rate. Inter-state supplies carry a single IGST at the full rate.
Is GST registration mandatory for small businesses?
Not until aggregate turnover crosses the threshold in section 22 — broadly ₹40 lakh for goods and ₹20 lakh for services, lower in special category states. Section 24 lists cases requiring registration regardless of turnover. Many register voluntarily to claim input credit or to satisfy corporate customers.
Is GST charged on export of services?
Export of services is zero-rated under section 16 of the IGST Act. You can file a Letter of Undertaking in Form GST RFD-11 and export without paying IGST, or pay and claim a refund. All conditions in section 2(6) of the IGST Act must be met, including payment received in convertible foreign exchange.
What if I charged the wrong GST rate on an invoice?
It is corrected through a credit or debit note under section 34 of the CGST Act, within the time limits set out there. Under-charging leaves the shortfall as your liability, so it is better fixed promptly than at year end.
What happens if I file my GST return late?
A late fee applies for each day of delay, subject to caps, and interest is payable on tax paid late. Continued non-filing can block the e-way bill facility and, in serious cases, lead to cancellation of registration. Our GSTR-3B interest calculator and GSTR-9 late fee calculator will estimate the amounts.