Learn the GST calculation formula for both inclusive and exclusive prices. Step by step examples for 5%, 18%, and 40% rates with a free online calculator.
There are two ways to calculate GST — and confusing them is one of the most common billing mistakes in India. Exclusive calculation adds GST on top of the base price: 'My product costs Rs 1,000, how much GST do I add?' Inclusive calculation extracts GST from a total price: 'The MRP is Rs 1,180, how much of that is GST?' Both use simple formulas, and our free GST calculator handles both instantly.
After the GST 2.0 reform, India has three main rates: 5% (essential goods), 18% (standard rate), and 40% (luxury and sin goods). The old 12% and 28% slabs were abolished in September 2025. This tutorial covers the calculation formula for all rates with worked examples. Use the reverse GST calculator for inclusive calculations.
This is the most common calculation — you know the price before tax and want to add GST.
Formula: GST Amount = Base Price × GST Rate / 100
Total Price = Base Price + GST Amount
Example 1 — 18% GST: You sell a laptop for Rs 50,000 (before tax). GST at 18% = Rs 50,000 × 18/100 = Rs 9,000. For intra-state: CGST = Rs 4,500, SGST = Rs 4,500. For inter-state: IGST = Rs 9,000. Total invoice = Rs 59,000.
Example 2 — 5% GST: You sell packaged food for Rs 200. GST at 5% = Rs 200 × 5/100 = Rs 10. CGST = Rs 5, SGST = Rs 5 (intra-state). Total = Rs 210.
Example 3 — 40% GST: A bottle of aerated drink for Rs 50. GST at 40% = Rs 50 × 40/100 = Rs 20. Total = Rs 70. This is the new luxury slab under GST 2.0.
Try it yourself: open the GST calculator, enter the amount, select the rate, and get instant results with CGST/SGST/IGST breakup.
When you see an MRP or a total amount and need to find out how much GST is included — this is the reverse calculation.
Formula: Base Price = Total Price × 100 / (100 + GST Rate)
GST Amount = Total Price - Base Price
Example 1 — 18% GST inclusive: A product has MRP Rs 1,180 including GST. Base Price = Rs 1,180 × 100 / 118 = Rs 1,000. GST = Rs 1,180 - Rs 1,000 = Rs 180. CGST = Rs 90, SGST = Rs 90.
Example 2 — 5% GST inclusive: Total amount Rs 525 including GST. Base = Rs 525 × 100 / 105 = Rs 500. GST = Rs 25. CGST = Rs 12.50, SGST = Rs 12.50.
Example 3 — 40% GST inclusive: Total Rs 700 including GST. Base = Rs 700 × 100 / 140 = Rs 500. GST = Rs 200.
Use our reverse GST calculator for instant inclusive calculations. It extracts the base price and GST amount from any total.
Effective from September 22, 2025
| Feature | GST Rate | Common Items |
|---|---|---|
| 0% (Exempt) | Fresh food, milk, curd, bread, life/health insurance (new under GST 2.0) | |
| 5% | Packaged food, soaps, medicines, footwear under Rs 1,500, economy air travel | |
| 18% | Most goods and services — electronics, furniture, IT services, telecom, restaurants | |
| 40% | Tobacco, aerated drinks, luxury cars above Rs 20L, sports bikes above 350cc | |
| Abolished: 12% | Items moved to 5% or 18% — no longer applicable | |
| Abolished: 28% | Items moved to 18% or 40% — no longer applicable |
Most invoices have multiple items at different GST rates. The calculation is item-by-item — you cannot average the rates.
Example invoice:
Item 1: T-shirt (HSN 6109) — Rs 800 × 2 qty = Rs 1,600 at 5% GST = Rs 80
Item 2: Laptop bag (HSN 4202) — Rs 2,000 × 1 qty = Rs 2,000 at 18% GST = Rs 360
Item 3: Wireless mouse (HSN 8471) — Rs 500 × 1 qty = Rs 500 at 18% GST = Rs 90
Invoice total: Subtotal Rs 4,100 + Total GST Rs 530 = Rs 4,630
Tax breakup (intra-state): CGST on 5% items = Rs 40. SGST on 5% items = Rs 40. CGST on 18% items = Rs 225. SGST on 18% items = Rs 225.
Each item's GST is calculated separately and then aggregated. The invoice shows the breakup by rate slab. This is how your GSTR-1 HSN summary table works — aggregating by HSN code and rate.
In myBillPlease, you add items to the invoice and the system calculates everything — per-item tax, per-rate totals, and the invoice grand total with correct CGST/SGST/IGST splits. Zero manual math.
Discounts change the taxable value — and GST is calculated on the value AFTER discount, not before.
Rule: If the discount is mentioned on the invoice and linked to the supply, GST applies on the discounted value. If the discount is given later (post-sale), you issue a credit note.
Example: Product price Rs 10,000. Discount 10% = Rs 1,000. Taxable value = Rs 9,000. GST at 18% = Rs 1,620 (not Rs 1,800). Total = Rs 10,620.
Wrong way: Some businesses calculate GST on the full price (Rs 1,800) and then subtract the discount. This overcharges the customer and creates ITC discrepancies.
In myBillPlease, enter the discount per item or as a percentage — the system recalculates the taxable value and GST automatically. The invoice shows the original price, discount, and tax on the discounted amount — exactly as GST rules require.
Avoid these errors that cause wrong invoices and compliance issues
If MRP already includes GST (inclusive price), you must extract GST using the reverse formula. Adding GST on top of MRP results in double taxation. Use the reverse GST calculator.
After GST 2.0 (Sep 2025), the 12% and 28% rates no longer exist. Using them on invoices is non-compliant. Update your product catalog to the new 5%, 18%, or 40% rates.
GST amounts should be rounded to 2 decimal places. For CGST and SGST, round each separately — don't round the total and split. Rs 127.50 becomes CGST Rs 63.75 + SGST Rs 63.75.
Always calculate GST on the price after applying the discount, not before. GST on pre-discount amount overcharges the customer and creates ITC mismatches.
An invoice must have either IGST or CGST+SGST — never both on the same invoice. If some items are inter-state and some intra-state, they need separate invoices.
Hundreds of items changed rates in September 2025. If you haven't updated your product GST rates since then, every invoice has wrong tax. Review your catalog now.
Why calculate manually when you can get instant, accurate results?
GST Calculator: Enter any amount and GST rate. Get instant CGST, SGST, and IGST breakup for both exclusive and inclusive calculations. Free, no signup.
Reverse GST Calculator: Enter the total amount including GST. Instantly get the base price and tax extracted. Perfect for MRP-based pricing.
myBillPlease Billing: Save products with GST rates. Every invoice auto-calculates tax — per item, per rate slab, with correct CGST/SGST/IGST splits. Free forever plan with unlimited invoices.
Both exclusive and inclusive calculations. CGST, SGST, IGST breakup. All GST 2.0 rates supported.
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