Discount calculator

Percent off: sale price = original price × (1 − discount% ÷ 100). An $80 shirt at 25% off is 80 × 0.75 = $60. Fixed off: sale price = original price − amount. The same $80 shirt with a $15-off coupon is $65.

Percent off scales with the price, which is why sitewide sales almost always use it. A fixed dollar coupon like "$10 off" is worth more, proportionally, on a cheaper item than an expensive one, which is why stores often set a minimum order value before it applies.

Discounts stack multiplicatively, not by adding the percentages. A 20% off sale plus a 10% off coupon is not 30% off. It's 20% off first, then 10% off what's left: $100 → $80 → $72, a 28% total discount, not 30%.

When one discount is a percent and one is a fixed dollar amount, the order changes the result. As a default, apply the percent discount first, then subtract the flat coupon, unless your store's coupon terms say otherwise.

If you only know the sale price and the discount, original price = sale price ÷ (1 − discount% ÷ 100). A $60 item marked "25% off" had an original price of 60 ÷ 0.75 = $80.

Before running a sale, check what margin survives it. A product that costs $30 and normally sells for $80 has a 62.5% margin; a 25% off sale drops the price to $60, still a healthy 50% margin. The same 25% off on a product with a $65 cost leaves almost nothing. Run the numbers through the profit margin calculator before setting a sale depth, not just this one.