Discount
calculator
30% off $80, what do you pay, what do you save, and what happens when they stack an extra 10% on top? Every sale-tag question, answered as you type.
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A few solid picks. As an Amazon Associate, Calculate.to earns from qualifying purchases, at no extra cost to you.
OSALO Desktop Calculator
Extra-large 12-digit LCD, giant buttons, solar + battery, the classic office desk workhorse.
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Helix Oxford Scientific
240-function scientific calculator for KS3–KS4 maths, with hard cover. Exam-friendly, plastic-free packaging.
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Casio fx-83GTCW+
The UK classroom-standard scientific calculator (also in pink), allowed in most UK exams.
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ROATEE Construction Calc
Feet-inch-fraction engineering calculator for carpenters, framers and contractors on site.
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Sale-tag math, done right
A discount multiplies the price by one minus the rate. The part people get wrong is stacking: "30% off, plus an extra 10%" is not 40% off, the second discount applies to the already-reduced price.
Effective discount: 37%, not 40%.
Going backwards
To recover the original price from a sale price, divide by (1 − discount), don't add the percent back, which undershoots. $56 after 30% off was $56 ÷ 0.70 = $80. Same trap as removing tax; the VAT calculator handles that side, and the percentage calculator covers every variation.
Discount FAQ
Multiply the price by one minus the discount as a decimal. 30% off $80 is 80 × 0.70 = $56, saving $24.
No. Each applies to the already-reduced price: 30% then 10% is 80 × 0.7 × 0.9 = $50.40, an effective 37%, not 40%.
Divide the sale price by one minus the discount. $56 after 30% off: 56 ÷ 0.7 = $80. Adding the percentage back gives the wrong answer.
Order doesn't matter, multiplication commutes, so 30% then 10% equals 10% then 30%. Only the combined multiplier counts.