How is GST calculated on a product?

Quick answer: Add GST: Price × (1 + GST rate). Remove GST: Price / (1 + GST rate).

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Full explanation

To add GST to a base price: Final price = Base price × (1 + GST rate). Example: ₹10,000 + 18% GST = ₹10,000 × 1.18 = ₹11,800. To find pre-GST price from a GST-inclusive price: Base price = Inclusive price / (1 + GST rate). Example: ₹11,800 inclusive of 18% GST → Base = ₹11,800 / 1.18 = ₹10,000. Common mistake: people subtract 18% from the inclusive price (₹11,800 × 0.18 = ₹2,124 — wrong). The correct GST in ₹11,800 is ₹11,800 × 18/118 = ₹1,800.