Adding or removing tax from a price sounds simple, but a lot of people get the "remove tax" calculation wrong — and it's an easy mistake to make if you don't know the correct formula.
Adding GST/Tax to a Price
To add tax, multiply the price by (1 + tax rate). For example, adding 10% tax to $100: 100 × 1.10 = $110. This part is usually intuitive and most people get it right.
Removing GST/Tax from a Price (The Common Mistake)
Here's where people go wrong: if a price already includes 10% tax, you can't just subtract 10% of the total to find the pre-tax price. Subtracting 10% of $110 gives you $99 — not $100. The correct formula is to divide by (1 + tax rate): 110 ÷ 1.10 = $100. This is because the 10% tax was calculated on the original $100, not on the final $110.
Add or remove GST/sales tax from any price instantly, with zero calculation errors.
🧾 Try the Free GST CalculatorWhy This Matters
- Invoicing: Correctly showing the tax-exclusive price on invoices and receipts
- Budgeting: Knowing the real pre-tax cost of a purchase
- Business pricing: Setting a price that nets the exact tax-exclusive amount you want after tax is added
- Expense reporting: Separating the tax portion from the actual cost for accounting purposes
Getting tax calculations wrong — even by a small percentage — adds up quickly across many transactions. Our free GST Calculator handles both adding and removing tax correctly, every time.