Find out what you actually pay after a discount, and how much you save. If GST applies, it is worked out on the discounted price.
The discount is calculated on the original price and subtracted from it.
If GST applies, it is charged on the discounted price, not the original — this is how invoices are raised under GST.
The saving is shown both as an amount and as a percentage.
Discount: Price × Discount% ÷ 100
Price after discount: Price − Discount
Final price: Discounted price + GST on that price
Is GST charged before or after the discount?
After. When a discount is shown on the invoice at the time of sale, GST is charged on the lower price. So a bigger discount lowers both the price and the tax.
How do I calculate two successive discounts?
Apply them one after the other, not by adding them together. Two 20% discounts in a row are not 40% off — they leave 0.8 × 0.8 = 0.64 of the price, which is actually 36% off.