Discount Calculator
Calculate sale prices, savings and discount percentages instantly
// Compare Discount Levels
| Discount | You Save | Sale Price | vs Current |
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How to Use the Discount Calculator
Choose what you want to calculate using the tabs above. Sale Price — enter the original price and discount percentage to find the sale price. Original Price — enter the sale price and discount percentage to work out what the original price was. Find % Off — enter both prices to calculate the discount percentage.
Discount Formulas
Stacked Discounts
When two discounts are applied sequentially — for example a 20% sale plus an extra 10% off — the combined discount is NOT simply 30%. The second discount is applied to the already-reduced price. Use the optional second discount field to see the true effective combined discount.
Finding the Original Price
If an item is on sale for £80 and you know it has a 20% discount, the original price is NOT £80 + 20% = £96. The correct calculation divides by (1 − 0.20) = £80 / 0.80 = £100. This calculator handles this correctly in "Original Price" mode.
Discount Math: What the Sale Sign Isn't Telling You
Built and verified by Andrius R. · Updated June 2026
Discount arithmetic is simple multiplication — which retailers count on you not doing. The same three formulas, plus the four standard pricing tricks they power.
The three directions
Sale price: 30% off $80 → 80 × (1 − 0.30) = $56. (Multiply by what you pay — 70% — rather than computing the discount and subtracting; one step, fewer errors.)
Discount percent: was $75, now $60 → (75 − 60) ÷ 75 = 20% off. The original price is always the denominator.
Original price (the reverse trap): paid $56 after 30% off → original = 56 ÷ 0.70 = $80, not 56 + 30% = $72.80. Same divide-don't-subtract logic as reverse VAT.
Stacked discounts never add
"Extra 20% off already-reduced items" on a 20%-off rack is not 40% off: you pay 0.80 × 0.80 = 64%, so the true discount is 36%. A "50% + 30%" stack is 65% off, not 80%. Sequential percentages multiply — and retailers phrase stacks additively precisely because the additive reading sounds bigger. (One mildly useful corollary: the order of stacked discounts never matters; 0.8 × 0.7 = 0.7 × 0.8.)
The pricing tricks the math exposes
- Anchoring: "Was $199, now $79" makes $79 feel like a gift — but the only number that matters is whether the item is worth $79 to you. Inflated "was" prices are the oldest trick on the tag, and regulators in many countries now require the reference price to be genuine (typically the lowest price of the prior 30 days in the EU) — a rule that exists because the trick works.
- "Up to 70% off": the legal load-bearing words are "up to" — one clearance item earns the banner while the rack averages 20%.
- Percent vs amount framing: shops quote whichever sounds larger — "$10 off!" on a $30 item (33%) but "25% off!" on a $400 one ($100). Convert to the other form before deciding; your brain weighs them differently.
- Spend-more-to-save: "$15 off $100" means spending $37 extra to save $15 if your basket was $63. A discount you stretched to reach is a markup wearing a costume.
Unit price: the comparison that beats every sale sign
Sales compare an item to its own past price; unit price compares it to alternatives, which is the comparison that actually saves money. A 500 g pack at $3.20 is 0.64/100 g; the 750 g "bigger value" pack at $4.50 is 0.60/100 g — genuinely cheaper, this time. But not always: shrinkflation and decoy sizing mean the large size is sometimes worse per unit, a pattern common enough that checking feels like catching someone. Most shelf labels print unit price in small type; reading it is the entire skill.
A two-second sanity kit
- 10% of anything = shift the decimal; build other percentages from it (30% = 3 × 10%).
- x% of y = y% of x when one direction is easier: 8% of 50 = 50% of 8 = 4.
- Final price multipliers: 25% off → ×0.75; 60% off → ×0.4. Thinking in "what I pay" multipliers makes stacking obvious too.
// Stacked ≠ Added
20% off then 10% off = 28% total — not 30%. Stacked discounts always give less than the sum of individual discounts.
// Original Price Trap
To find the original from a sale price, divide by (1 − discount). Don't add the % back — that gives the wrong answer.
// Biggest Bang
Apply the largest discount first — it saves slightly more in absolute terms because it applies to the highest starting price.
// Price Anchoring
Retailers often inflate "original" prices to make discounts look bigger. Compare the sale price to other retailers, not just the crossed-out price.