How to add sales tax to a price
Multiply the price by the tax rate and add it on: Total = Price × (1 + rate ÷ 100). For example, a 100 item at 17% tax becomes 100 × 1.17 = 117, with 17 of tax.
How to remove tax from a total (reverse VAT)
If a price already includes tax and you want the original, divide by (1 + rate ÷ 100): Pre-tax = Total ÷ (1 + rate ÷ 100). So a 117 tax-inclusive total at 17% was 117 ÷ 1.17 = 100 before tax, with 17 of tax. This is handy for invoices, expense claims and checking receipts.
Sales tax vs VAT vs GST
They're variations on the same idea — a percentage added to goods and services. Sales tax (US) is added at the till; VAT (UK, EU, Pakistan) and GST (India, Australia, Canada) are usually built into displayed prices. Rates differ by country and item, so enter your local rate.
Is the tax on the pre-tax or post-tax price?
Always on the pre-tax price. That's why removing tax means dividing by (1 + rate), not just subtracting the percentage.
Why isn't "remove 17%" the same as subtracting 17%?
Because the 17% was added to the smaller pre-tax number. Subtracting 17% of the larger total takes off too much — you must divide instead.