What is the GST Calculator?
GST is charged on almost every sale of goods and services in India, and people run into it from two directions. A business quoting ₹50,000 plus GST needs the tax added on top. Someone holding a bill that already includes GST wants to know how much of it is tax. These are different calculations, and the same numbers give different answers in each.
This calculator works in both directions with any rate you enter, including the 5%, 18% and 40% rates in use since GST was restructured in September 2025. It also splits the tax the way an invoice shows it: equal CGST and SGST when the sale stays inside one state, or a single IGST charge when it crosses a state border.
What each input means
- This amount is
- Choose “Before GST” for a price or quote that does not include tax yet, so GST is added on top. Choose “Including GST” for a bill total, an MRP or any price that already contains the tax, so the tax inside it is separated out.
- Amount
- The price, quote or invoice value you are starting from.
- GST rate
- The rate for what is being sold. It follows the item’s HSN code for goods or SAC code for services, not the kind of business selling it, so one shop can charge several rates on a single bill.
- This sale is
- Within one state, the tax is split equally into CGST for the central government and SGST for the state. For a buyer in another state, or for imports, the same total is charged as IGST. This changes how the tax is shown on the invoice, never how much it is.
How this calculation works
Adding GST is one multiplication. The tax is the amount times the rate, and the bill is the amount plus that tax. At 18%, ₹10,000 carries ₹1,800 of GST and comes to ₹11,800.
Taking GST out of a price works backwards. An inclusive price at 18% is 118% of the pre-tax value, so dividing ₹11,800 by 1.18 returns ₹10,000, and the ₹1,800 difference is the tax. Applying 18% to ₹11,800 instead gives ₹2,124, which is ₹324 too much. In general, tax makes up rate ÷ (100 + rate) of any GST-inclusive price: 15.25% at 18%, 4.76% at 5% and 28.57% at 40%. The calculator shows that share with every result.
The split never changes the total. A sale inside one state divides the GST into two equal halves, so 18% appears on the invoice as 9% CGST and 9% SGST. A sale to a buyer in another state carries the full 18% as IGST, which the centre collects and later shares with the state where the goods or services are used.
Formula: GST added = amount × rate; GST inside a price = price − price ÷ (1 + rate); within a state CGST = SGST = GST ÷ 2, between states IGST = GST
What ₹10,000 looks like at each GST rate
Worked out with this calculator’s formulas and rounded to the rupee. The last column is the one people get wrong: the tax share of a GST-inclusive price is always smaller than the rate.
| Rate | Adding GST to ₹10,000 | Taking GST out of ₹10,000 | Share of the final price |
|---|---|---|---|
| 3% | ₹300 GST ₹10,300 total | ₹291 GST ₹9,709 before GST | 2.91% |
| 5% | ₹500 GST ₹10,500 total | ₹476 GST ₹9,524 before GST | 4.76% |
| 18% | ₹1,800 GST ₹11,800 total | ₹1,525 GST ₹8,475 before GST | 15.25% |
| 40% | ₹4,000 GST ₹14,000 total | ₹2,857 GST ₹7,143 before GST | 28.57% |
Getting the most out of the result
- Check whether a figure includes GST before working anything out. Quotes between businesses usually exclude it and say “+ GST”, while shop prices and MRPs include it.
- Look up the rate by HSN code for goods or SAC code for services in the rate notifications CBIC publishes, not by the product’s everyday name. Items that sound alike can sit in different slabs.
- If a price list, invoice template or billing software was set up before 22 September 2025, recheck every item. Most items that were at 12% or 28% have since moved to 5%, 18% or 40%.
- Match the tax to where the buyer is: CGST and SGST for a buyer in your state, IGST for one in another state. Fixing the wrong choice later takes a fresh payment and a refund claim.
- Pick one rounding rule, either tax on each line or tax on the invoice total, and use it on every invoice. Mixing the two leaves small gaps between your invoices and your returns.
- Before counting on input tax credit, check that the supplier’s invoice appears in your GSTR-2B. The credit generally depends on the supplier having reported the sale.
Common mistakes to avoid
The costliest error is finding the tax inside an inclusive price by applying the rate to it. The answer comes out too high by the rate itself: 18% too high at an 18% rate, 40% too high at 40%. On a ₹1 lakh inclusive bill at 18%, that is ₹18,000 of supposed tax against a real ₹15,254.
Businesses also charge CGST and SGST on a sale to another state, or IGST on a local one. Tax paid under the wrong head is not simply moved across: the correct tax has to be paid, and the wrong payment is recovered through a refund claim, which holds up cash in the meantime. Two more mistakes come up often. Small businesses under the composition scheme sometimes add GST to their bills, which the scheme does not allow. And some businesses count the GST they collect as revenue and overstate their income, when that money belongs to the government and only passes through their account.
Frequently asked questions
How do I remove GST from a price that already includes it?
Divide the price by 1 plus the rate written as a decimal, then subtract. For ₹5,900 at 18%, ₹5,900 ÷ 1.18 = ₹5,000 before GST, so the GST is ₹900: ₹450 each of CGST and SGST for a sale within one state. Taking 18% of ₹5,900 would give ₹1,062, which overstates the tax by 18%.
What are the GST rates in India now?
Since 22 September 2025, most goods and services are taxed at 5% or 18%. A 40% rate covers a short list that includes sweetened or flavoured aerated drinks, larger cars, motorcycles above 350cc, yachts and private aircraft, and, from 1 February 2026, most tobacco products and pan masala. Gold and silver are taxed at 3%. Many essentials are exempt, including fresh milk and vegetables, most healthcare services and, since the same September date, individual life and health insurance premiums. The GST Council can change any of these, so confirm the rate for your item’s HSN or SAC code before you invoice.
When is it CGST and SGST, and when is it IGST?
It depends on where the supply takes place compared with where the seller is registered. If both are in the same state, the invoice shows CGST and SGST, each at half the rate. If they are in different states, or the goods are imported, it shows IGST at the full rate. For goods, the place of supply is usually where delivery ends. For services sold to a registered business, it is usually where that business is registered. The total tax is the same either way.
What is UTGST?
The Union Territory version of SGST. In Union Territories without their own legislature, such as Chandigarh, Ladakh and Lakshadweep, a local sale carries CGST plus UTGST instead of CGST plus SGST, at the same combined rate. Delhi, Puducherry and Jammu and Kashmir have legislatures and use SGST. To calculate it, choose “Within one state” and read the SGST line as UTGST.
What is input tax credit and how does it change what a business pays?
It lets a registered business subtract the GST it paid on purchases from the GST it collects on sales. A trader who buys stock for ₹10,000 plus ₹1,800 GST and sells it for ₹15,000 plus ₹2,700 GST pays the government only the ₹900 difference, which is 18% of the ₹5,000 of value it added. The credit generally needs a valid tax invoice that also shows up in the buyer’s GSTR-2B.
When does a business have to register for GST?
In most states, once turnover in a financial year crosses ₹40 lakh for a business that supplies only goods, or ₹20 lakh for one that supplies services. A few north-eastern and hill states set lower limits. Some businesses must register whatever their turnover, including those selling goods to buyers in other states. Registering voluntarily below the limit is allowed, and a business has to be registered to claim input tax credit.
Do businesses under the composition scheme charge GST?
No. The scheme lets small businesses with turnover up to ₹1.5 crore (₹75 lakh in some states) pay a flat share of turnover instead: 1% for manufacturers and traders and 5% for restaurants, with a separate 6% option for small service providers. They issue a bill of supply with no GST on it and cannot claim input tax credit, so their prices have no GST line to separate out.
Is GST included in the MRP?
Yes. The maximum retail price printed on packaged goods has to include all taxes, so GST is never added on top of it at the till. To see how much of an MRP is tax, choose “Including GST” and enter the MRP with the item’s rate.
Is GST charged before or after a discount?
After a discount shown on the invoice at the time of sale: GST is charged on the reduced price. A discount given later, such as a year-end volume rebate, reduces the taxable value only in limited cases, typically when it is passed on through a GST credit note and the buyer reverses the matching input tax credit. Otherwise the tax stays on the original invoice value.
Why does the calculator show GST as a share of the final price?
Because that share is always lower than the rate, and mixing up the two is the most common GST error. At 18%, tax is 18 parts in every 118 of an inclusive price, or 15.25%. At 5% it is 4.76%, and at 40% it is 28.57%. If you know an inclusive total and only need the tax, multiplying by this share gets you there in one step.