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Percentage · lesson 18 of 20 · free

GST and tax: adding a percent — How to calculate percentage

A tax such as GST is a percent added on top of a price. Find the tax as a percentage of the price, then add it. If you know the price before and after tax, you can work back to the tax rate.

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How to work it out

Add it on — “total = price + rate% of the price”

  1. Tax = rate% of the price before tax.
  2. Total = price + tax. Shortcut: 18% GST means you pay 118% of the price.
  3. Tax rate = tax ÷ price before tax × 100.

Use it for: Shop and restaurant bills, online shopping, and the Class 8 sales-tax sums.

Worked example: A cricket bat costs ₹1200 plus 18% GST. What is the total price, in rupees? → 1416

  1. 18% of 1200 = 18 × 1200 ÷ 100.
  2. 18 × 1200 = 21600. Divide by 100 (take away two zeros): 21600 ÷ 100 = 216.
  3. Total = price + tax = 1200 + 216 = 1416.

Check: 118% of 1200 = 118 × 12 = 1416 ✓

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✓ Written and checked by the TalentJR team · Updated 13 Oct 2026 · How we make our lessons

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🖨️ GST Calculation Worksheet

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