GST on Everything: How to Add and Remove GST in 10 Seconds

Published 29 June 2026 · GST & TDS

Vikram had dinner at a restaurant in Bengaluru. The menu said his order — a biryani and a lassi — cost ₹1,200. The bill said ₹1,260. The extra ₹60 puzzled him. He asked the waiter, who said "GST, sir." That was the complete explanation. Two formulas — one to add GST, one to remove it — answer every GST question Vikram will ever have, whether he is at a restaurant, buying a laptop, or sending a freelance invoice.

Formula 1 — Adding GST to an Amount

Amount with GST = Original Amount × (1 + GST rate / 100)

Vikram's bill: ₹1,200 × (1 + 5/100) = ₹1,200 × 1.05 = ₹1,260. The ₹60 is exactly 5% of ₹1,200. Restaurants in India charge 5% GST (both AC and non-AC). Mystery solved.

The formula works for any GST rate. Buying a pair of jeans for ₹1,500 at 12% GST? ₹1,500 × 1.12 = ₹1,680. Engaging an IT consultant at ₹50,000 for 18% GST? ₹50,000 × 1.18 = ₹59,000. One formula, all rates.

Formula 2 — Removing GST from a GST-Inclusive Amount

Original Amount = GST-inclusive amount / (1 + GST rate / 100)

Suppose a laptop is listed at ₹1,00,000 inclusive of 18% GST. What is the base price before GST?

Original = ₹1,00,000 / 1.18 = ₹84,745.76.
GST amount = ₹1,00,000 – ₹84,745.76 = ₹15,254.24.

A common mistake is calculating 18% of ₹1,00,000 (= ₹18,000) and subtracting it to get ₹82,000. That is wrong. If the GST is already included, the base is smaller than the total — so you divide, not subtract.

GST Rates Quick Reference

Note: alcohol is taxed under state excise duty, not GST. Petroleum products are also outside GST. When in doubt, check the HSN code or SAC code for the specific product or service.

CGST, SGST and IGST — The Split Explained

GST has two modes. For transactions within the same state (intra-state), the total GST is split equally between the central government and the state government. For transactions across states (inter-state), the full amount goes as IGST to the central government, which then distributes it.

Intra-state example: A freelance graphic designer in Karnataka invoices a client in Karnataka for ₹50,000. GST rate for design services = 18%. Invoice total = ₹50,000 × 1.18 = ₹59,000. The GST portion of ₹9,000 splits as: CGST ₹4,500 + SGST ₹4,500.

Inter-state example: Same designer, client in Maharashtra. Invoice total = ₹59,000. The ₹9,000 goes as IGST ₹9,000. No split — the full amount goes to central government first.

This distinction matters for businesses claiming Input Tax Credit (ITC). CGST credit can only offset CGST liability; SGST credit only SGST; IGST can offset any liability. Mixing them up creates compliance issues.

What Suppliers Don't Always Tell You

GST calculation errors on supplier invoices are more common than most business owners realise. When a supplier sends you an invoice for ₹1,00,000 + 18% GST, the GST line should read exactly ₹18,000. If it reads ₹17,800 or ₹18,200, the invoice is wrong — and if you are GST registered and claiming Input Tax Credit on that invoice, the mismatch will show up in your GSTR-2B and create a reconciliation headache. Verify every invoice with Formula 1 before uploading it to your accounting software. It takes five seconds and can save hours of GST portal corrections.

Frequently Asked Questions

How do you add GST to an amount?

Amount with GST = Original Amount × (1 + GST rate / 100). Example: ₹1,000 + 18% GST = ₹1,000 × 1.18 = ₹1,180.

How do you remove GST from a GST-inclusive amount?

Original Amount = GST-inclusive amount / (1 + GST rate / 100). Example: If ₹1,180 includes 18% GST, original = ₹1,180 / 1.18 = ₹1,000. GST amount = ₹180.

What are the GST rates in India?

GST rates in India are 0% (essentials like vegetables, milk), 5% (packaged food, restaurants), 12% (processed food, medicines), 18% (most services, electronics, clothing above ₹1,000), and 28% (luxury goods, automobiles, tobacco).

What is the difference between CGST, SGST and IGST?

For intra-state transactions, the total GST is split equally into CGST (central) and SGST (state). For inter-state transactions, IGST (integrated) applies at the full rate. Example: 18% GST sold within Maharashtra = 9% CGST + 9% SGST. Sold from Maharashtra to Delhi = 18% IGST.

Is GST charged on restaurant food in India?

Yes — restaurants charge 5% GST (both AC and non-AC premises). Restaurants in 5-star hotels charge 18% GST. Alcohol is taxed separately under state excise duty, not GST.

Are you GST registered and claiming ITC — or a consumer who just wants to verify their bills? Both use the same two formulas.