How Discount Calculations Work
Understanding how discounts are applied helps you make smarter purchasing decisions and spot misleading "deals." This calculator handles three types of price reductions, applied in order:
- Percentage discount is applied first:
Discounted = Price × (1 - Discount%/100) - Flat discount is subtracted next:
After Flat = Discounted - Flat Amount - Tax is added last:
Final = After Flat × (1 + Tax%/100)
This order matters. If tax were calculated before the discount, you would pay more. Most jurisdictions require tax to be calculated on the post-discount price.
Common Discount Types Explained
Percentage Discount
The most common type. "25% off" means you pay 75% of the original price. A $120 item at 25% off costs $90. Retailers often use percentage discounts because the absolute savings look smaller than they feel — $30 off $120 sounds less impressive than "25% off" even though it is the same thing.
Flat Discount
A fixed dollar amount off, regardless of the original price. "$20 off any purchase" is a flat discount. These are common in coupons and mail-in rebates. They are more beneficial on lower-priced items where a percentage discount would save less.
Stacked Discounts
When stores offer "30% off plus an extra 15% off," the discounts are not additive (not 45%). The second discount applies to the already-reduced price. For a $100 item: first 30% off = $70, then 15% off $70 = $59.50. The effective discount is 40.5%, not 45%. This calculator handles this correctly when you enter the percentage discount as the combined effect.
Tax on Discounted Items
Sales tax is generally calculated on the price you actually pay after discounts, not the original price. A $100 item at 20% off ($80) with 8% tax costs $86.40 — not $86.40 (which would be the case if tax were calculated on $100). This calculator applies tax after all discounts, which is the standard practice.
Tips for Smart Shopping
- Compare the final price, not the discount percentage — 50% off an inflated price may still be a bad deal
- Stack coupons with sale prices for maximum savings
- Remember that tax applies after discounts in most places
- Watch for "minimum purchase" requirements on percentage-off coupons
- Flat discounts are better on cheaper items; percentage discounts are better on expensive ones