GST Calculation Explained: Inclusive vs Exclusive, CGST, SGST, IGST
Add or remove GST with two simple formulas. Worked rupee examples for inclusive and exclusive prices, plus when CGST+SGST or IGST applies.
To add GST to a price, multiply it by (1 + rate/100). To remove GST from a price that already includes it, divide by (1 + rate/100). For example, ₹1,000 plus 18% GST is ₹1,180, and a ₹1,180 price that includes 18% GST has a base price of ₹1,000 and ₹180 of tax.
Whether that tax appears on the bill as CGST + SGST or as IGST depends only on whether the sale is within one state or between two states. The total amount is the same either way.
Our GST calculator does both directions instantly and shows the CGST/SGST split.
The two formulas
GST exclusive (price before tax is known)
- GST amount = price x rate / 100
- Total = price + GST amount
GST inclusive (final price is known)
- Base price = total x 100 / (100 + rate)
- GST amount = total - base price
A quick way to find the tax inside an inclusive price: GST = total x rate / (100 + rate).
A very common mistake is to take 18% of the inclusive price and subtract it. 18% of ₹1,180 is ₹212.40, which is wrong. The tax inside ₹1,180 is only ₹180, because the 18% was applied to ₹1,000, not to ₹1,180.
Worked examples
Example 1: exclusive, 18%
A service is quoted at ₹25,000 plus GST at 18%.
- GST = 25,000 x 18 / 100 = ₹4,500
- Total = ₹29,500
Example 2: inclusive, 18%
A gadget is sold for ₹5,900 including 18% GST.
- Base price = 5,900 x 100 / 118 = ₹5,000
- GST = 5,900 - 5,000 = ₹900
Example 3: inclusive, 5%
A packaged food item costs ₹500 including 5% GST.
- Base price = 500 x 100 / 105 = about ₹476.19
- GST = about ₹23.81
Example 4: discount before GST
An item is priced at ₹2,000 before tax with a 10% discount and 18% GST.
- After discount = ₹1,800 (try this in the discount calculator)
- GST = 1,800 x 18 / 100 = ₹324
- Total = ₹2,124
Generally, a discount shown on the invoice at the time of sale reduces the value on which GST is charged.
CGST, SGST, UTGST and IGST
GST in India has a few components, but you never pay more than the one stated rate.
| Type of sale | Taxes on the invoice | Example at 18% on ₹1,000 |
|---|---|---|
| Within one state (intra-state) | CGST + SGST, split equally | CGST ₹90 + SGST ₹90 |
| Within a union territory without its own legislature | CGST + UTGST, split equally | CGST ₹90 + UTGST ₹90 |
| Between two states (inter-state), and imports | IGST | IGST ₹180 |
- CGST goes to the central government.
- SGST (or UTGST) goes to the state or union territory.
- IGST is collected by the centre on inter-state supplies and later shared with the destination state.
The deciding question is whether the supplier's location and the place of supply are in the same state. A shop in Pune selling to a customer in Pune charges CGST + SGST. The same shop shipping to a customer in Bengaluru charges IGST. The place of supply rules can get detailed for services, so businesses with unusual cases should check with a tax professional.
Current GST rate structure
The GST Council rationalised the rates with effect from 22 September 2025. Most items now fall into:
- 0% (exempt or nil-rated), for example many fresh food items
- 5% for many essentials
- 18% as the standard rate for most goods and services
- 40% for certain luxury and sin goods
The older 12% and 28% slabs were largely removed, with most items moved to 5% or 18%. A few goods, such as gold, have their own special rates, and some products had transitional arrangements. Rates for a specific item are set by official notifications, so check the CBIC rate schedule or your supplier's invoice rather than relying on a general list.
How GST appears on a proper invoice
A GST invoice from a registered business usually shows:
- The taxable value (price before GST)
- The rate and the amount of each tax (CGST and SGST, or IGST)
- The total invoice value
- The HSN code for goods or SAC code for services
- The supplier's GSTIN, and the buyer's GSTIN for business purchases
If a bill only shows a total with "GST included" and no breakup, you can use the inclusive formula above to work out the tax yourself.
Using percentages for quick mental checks
- 18% of a number is 10% + 8%. For ₹3,500: ₹350 + ₹280 = ₹630.
- 5% is half of 10%. For ₹3,500: ₹175.
- To remove 18% GST mentally, divide by 1.18. Dividing by 1.2 gives a quick rough figure, but it is slightly too low, so use a calculator for anything official.
For any other percentage sum, the percentage calculator is handy.
Common mistakes
- Subtracting 18% from an inclusive price. Divide by 1.18 instead.
- Adding CGST and SGST as if each were the full rate. They are halves of one rate.
- Charging CGST + SGST on an inter-state sale. That needs IGST.
- Using an old rate list. Many items moved slabs in September 2025.
- Rounding each line differently. Work out tax per line and round consistently, or your invoice totals may not match.
- Applying GST before the discount when the discount is shown on the invoice. Discount first, then tax.
With the two formulas and the same-state rule, almost every everyday GST question can be answered in under a minute.
Questions
How do I remove 18% GST from a total price?
Divide the total by 1.18 to get the price before tax. The GST is the total minus that figure. For ₹1,180, the base price is ₹1,000 and the GST is ₹180.
What are the GST rates in India now?
Since 22 September 2025, most goods and services fall under 0%, 5% or 18%, with a 40% rate for certain luxury and sin goods. A few items, such as gold, have special rates. Check the official CBIC rate schedule for a specific item.
Is CGST and SGST charged on top of each other?
No. For an intra-state sale, the GST rate is simply split into two equal halves. 18% GST becomes 9% CGST plus 9% SGST, not 18% plus 18%.
When is IGST charged instead of CGST and SGST?
IGST applies when the supplier and the place of supply are in different states, and on imports. CGST plus SGST applies when both are in the same state.