How do I remove GST from a total amount?

Divide, do not subtract. To extract 18% GST from ₹1,180, calculate 1180 × 100 ÷ 118 = ₹1,000 as the taxable value, leaving ₹180 of GST. Simply taking 18% off ₹1,180 gives ₹967.60, which is wrong by ₹32.40 — because the 18% was charged on the base value, not on the total.

What is the difference between CGST, SGST and IGST?

The total tax is identical; only the split differs. When the supplier and the customer are in the same state it is an intra-state supply and the tax is divided equally into CGST for the Centre and SGST for the state — 18% becomes 9% plus 9%. When they are in different states it is an inter-state supply and the whole 18% is charged as a single IGST. Get the split wrong on an invoice and your customer cannot claim input tax credit until it is amended.

What are the GST rates in India?

The main slabs are 0%, 5%, 12%, 18% and 28%. Essentials such as unbranded food grains are nil-rated, 5% covers most packaged food and economy transport, 12% and 18% cover the bulk of goods and services with 18% being the standard rate, and 28% applies to luxury and sin goods, often with an additional compensation cess on items like cars, tobacco and aerated drinks.

Is GST calculated on the amount before or after discount?

On the amount after discount, provided the discount is shown on the invoice at the time of supply. A discount given later is only deductible if it was agreed before the supply and can be linked to the specific invoices. Otherwise GST stays payable on the full pre-discount value.

Free Calculator

GST Calculator

Add GST to a price, or pull the GST back out of a total that already includes it — with the CGST, SGST and IGST split worked out for you.

Your figures

What do you want to do? Add GST — I have the price before tax Remove GST — I have the total including tax

Amount before GST

GST rate

0% 5% 12% 18% 28%

Type of supply Intra-state — same state, split into CGST + SGST Inter-state — different states, charged as IGST

Your result

Total, including GST

₹11,800.00

₹1,800.00 of GST at 18%, added to ₹10,000.00.

GST breakdown — intra-state supply
Taxable value	₹10,000.00
CGST @ 9% (to the Centre)	₹900.00
SGST @ 9% (to Andhra Pradesh)	₹900.00
Total GST	₹1,800.00
Invoice total	₹11,800.00

An estimate for guidance, not tax advice. Compensation cess on items such as cars, tobacco and aerated drinks is charged over and above the rates here and is not included.

Reverse GST: the calculation everyone gets wrong

Adding GST is easy. A ₹1,000 item at 18% becomes ₹1,180 — everyone gets that right.

Going backwards is where it falls apart. Given a ₹1,180 total, the instinct is to take 18% off: ₹1,180 − ₹212.40 = ₹967.60. That is wrong, and it is wrong by ₹32.40.

The reason is that the 18% was never charged on ₹1,180. It was charged on ₹1,000. So to reverse it you must divide, not subtract:

Taxable value = Total × 100 ÷ (100 + rate)

GST = Total − Taxable value

For ₹1,180 at 18%: 1180 × 100 ÷ 118 = ₹1,000, leaving ₹180 of GST. That is the figure that goes on your invoice and into your return.

The divisors, if you prefer to do it in your head

Rate	Divide the total by	Or: GST as a share of the total	₹1,000 inclusive becomes
5%	1.05	4.762%	₹952.38 + ₹47.62 GST
12%	1.12	10.714%	₹892.86 + ₹107.14 GST
18%	1.18	15.254%	₹847.46 + ₹152.54 GST
28%	1.28	21.875%	₹781.25 + ₹218.75 GST

Note how far the second column is from the headline rate. At 28%, the GST inside a tax-inclusive price is 21.875% of that price, not 28%. That gap is exactly the error being made whenever someone subtracts instead of dividing.

When you need the reverse calculation

MRP-based retail. The price on the label includes GST. To book the sale you must split it into value and tax.
A supplier quotes "all inclusive". You need the taxable value to claim input tax credit correctly.
Cash sales without an invoice trail. Reconstructing the taxable value from collections at year end.
Composition to regular transition. Restating turnover that was previously recorded gross.

CGST, SGST and IGST — the split that trips up new registrants

GST is one tax collected in two ways, depending on whether the supply crosses a state border. The total is always the same. Which boxes it goes in is not.

Intra-state: same state, split in half

A Guntur business selling to a customer in Vijayawada is supplying within Andhra Pradesh. The 18% is divided equally: 9% CGST to the Central Government, 9% SGST to Andhra Pradesh. Both appear as separate lines on the invoice.

Inter-state: different states, one tax

The same Guntur business selling to a customer in Hyderabad is making an inter-state supply. The whole 18% is charged as IGST, collected by the Centre and later apportioned to the consuming state. One line on the invoice, not two.

How to tell which applies

It turns on the place of supply, not where you happen to be sitting. For goods, that is generally where the goods are delivered. For services it is usually the recipient's location if they are registered, and the supplier's location if they are not. Exports and supplies to a Special Economic Zone are zero-rated: no GST, but the input credit stays claimable.

Getting this wrong is a real problem, not a technicality. Charge CGST and SGST on what was actually an inter-state supply and your customer cannot claim the credit — the tax sits in the wrong state's ledger. Fixing it means a credit note, an amended return, and interest if it crosses a filing period.

The GST rate slabs

Rate	Typically applies to
0% / exempt	Unbranded food grains, fresh vegetables and fruit, milk, healthcare and education services.
5%	Packaged and branded food, tea and coffee, economy air travel, small restaurants, life-saving drugs.
12%	Processed food, business-class air travel, hotel rooms in the mid range, works contracts.
18%	The standard rate. Most services, professional and consultancy fees, telecom, IT services, industrial goods.
28%	Luxury and sin goods — cars, tobacco, aerated drinks, premium hotel rooms. Usually plus a compensation cess.

Rates are notified per HSN code for goods and SAC code for services, and they do change. If your product sits near a boundary, confirm the classification before you build a price around it — a reclassification from 12% to 18% applied retrospectively is an expensive surprise.

A few things worth knowing

GST is charged after discount, as long as the discount is on the invoice at the time of supply. A discount given afterwards only reduces GST if it was agreed beforehand and can be tied to specific invoices.
Registration is compulsory above ₹40 lakh of turnover for goods and ₹20 lakh for services in most states, and immediately for anyone making inter-state supplies or selling through an e-commerce platform, whatever the turnover.
Reverse charge shifts liability to the buyer for certain supplies — legal services from an advocate, goods transport, and purchases from unregistered dealers in defined cases. The buyer pays the tax directly and claims it back as credit.
Compensation cess sits on top of 28% for cars, tobacco and aerated drinks, at rates from 1% to 22%. This calculator does not include it.

If you are unsure which rate or which split applies to what you sell, ask us on WhatsApp — a two-minute answer now is considerably cheaper than an amendment later.