Percent Off Calculator

Background.

A percent off calculator answers the single most common piece of retail math there is: if a $80 item is 25% off, what do I actually pay? Enter the price and the discount percentage, and this page returns the final price and the exact amount you save, computed with arbitrary-precision decimal arithmetic so that a price like $59.99 at 15% off returns exactly $50.9915 — which rounds cleanly to $50.99 at the register — rather than a floating-point value with a stray trailing digit.

This page is intentionally narrow, and Quanta already ships a more comprehensive discount calculator that layers sales tax on top of the discounted price and walks through BOGO ("buy one get one") offer math in depth. The two pages are meant to be used differently. The full discount calculator is the right tool when you need the tax-inclusive total you'll actually be charged at checkout, or when you're trying to decode a "buy one get one 50% off" style promotion. This page is the fast version: no tax field, no BOGO essay, just price and percentage in, sale price and savings out — built for the person who typed "20 percent off calculator" into a search bar mid-shopping-trip and wants an answer in one glance, not a six-field form.

What this page adds that the fuller discount calculator does not is a second, optional stacked-discount field, because "what's 30% off, then an extra 20% off" is one of the most frequently miscalculated numbers in retail. The intuitive but wrong answer is 50% off. The correct answer is 44% off, because the second discount applies to the already-reduced price, not the original one: a $200 item at 30% off is $140, and $140 with a further 20% off is $112 — a combined saving of $88, or 44% of the original $200, not 50%. Retailers are not being deceptive when they advertise stacked percentages this way; the arithmetic simply compounds multiplicatively rather than adding linearly, and this calculator computes the true combined rate for you instead of making you run the tool twice.

The underlying skill here — using proportional reasoning to solve percent problems involving markups and markdowns — is named explicitly in the Common Core State Standards for Mathematics, which group percent-off ("markdown") problems together with sales tax, tips, and commissions as core applications of seventh-grade ratio reasoning. The Federal Trade Commission's Guides Against Deceptive Pricing, at 16 CFR Part 233.1, separately governs the legal side of this arithmetic: for a "was $X, now Y% off" claim to be lawful, the "was" price has to be a real price the item was actually offered at for a reasonably substantial period, not an inflated number invented the week before a sale specifically to make the percentage look bigger. This calculator does not — and cannot — verify whether a sticker price is honest; it can only tell you, correctly, what the advertised percentage actually does to that price once you trust the starting number.

One domain boundary worth stating plainly: a discount percentage above 100% is not meaningful (you cannot be paid more than the item's full price as a "discount" within this formula) and a negative discount is not a discount at all — it would be a markup, which is a different calculation with a different formula. Both of the discount fields on this page are therefore restricted to the 0–100% range, and the calculator throws a clear validation error rather than silently producing a nonsensical negative sale price if you try to enter something outside it.

Below the calculator you'll find the exact formula, a hand-verified stacked-discount example, and eight FAQs covering the stacking trap, currency rounding, the difference between this page and the full discount calculator, and how percent-off relates to markup and profit margin on the seller's side of the same transaction.

What is percent off calculator?

Percent off is a multiplicative discount applied to a stated original price: paying (100 − discountPercent) cents of every dollar of the original price. Formally, finalPrice = price × (1 − discountPercent ÷ 100). This is the retail application of the same proportional-reasoning skill named in Common Core State Standard 7.RP.A.3, which explicitly groups markdowns (percent-off discounts) with markups, sales tax, tips, and commissions as instances of "multistep ratio and percent problems." When a second discount is stacked on top of the first — a store discount plus a manufacturer coupon, or a clearance markdown plus a loyalty-program discount — the two percentages do not add together. Each discount is applied, in turn, to whatever price remains after the previous one, which is why two 20% discounts stacked together produce a 36% total saving (1 − 0.80 × 0.80 = 0.36), not 40%. This calculator's optional second-discount field exists specifically to make that compounding visible and correctly computed, rather than left as a mental-math trap.

How to use this calculator.

1. 01Enter the original price of the item.
2. 02Enter the discount percentage — for "30% off" enter 30, not 0.30.
3. 03If a second discount stacks on top (an extra coupon, a clearance markdown, a loyalty discount), enter it in the second field. Leave it at 0 if there's only one discount.
4. 04Read the final price — what you'd owe before any sales tax is added.
5. 05Read "you save" for the dollar amount removed from the original price, and the combined effective discount for the true total percentage once both discounts are stacked.
6. 06If you need the tax-inclusive total, or you're trying to decode a BOGO-style offer, use the full discount calculator instead — this page deliberately leaves tax out so the core percent-off math stays fast and unambiguous.

The formula.

The core relationship is finalPrice = price × (1 − discountPercent ÷ 100). Subtracting the discount rate from 1 and multiplying is algebraically identical to computing the discount amount and subtracting it — a $80 item at 25% off is either 80 × (1 − 0.25) = 80 × 0.75 = $60, or equivalently 80 − (80 × 0.25) = 80 − 20 = $60 — but the multiplicative form is faster and is what point-of-sale systems compute internally.

When a second discount is present, it is applied to the already-discounted price, not the original: finalPrice = price × (1 − d₁ ÷ 100) × (1 − d₂ ÷ 100). This is why stacked percentages compound rather than add. A $200 item at 30% off becomes $140 after the first discount; applying a further 20% off to that $140 (not to the original $200) removes another $28, landing at $112. The total saved is $88 out of $200, which is a combined effective discount of 44%, not the naively-summed 50%. The gap between the naive sum and the true compounded rate grows as the individual discount percentages grow, which is why the effect is most visible — and most often gotten wrong — during steep clearance sales that stack a markdown with a coupon.

amountSaved is simply price minus finalPrice, in the same currency units you entered. combinedDiscountPercent re-expresses that saving as a single percentage of the original price — amountSaved ÷ price × 100 — so you can compare a stacked two-discount offer against a single flat discount on an apples-to-apples basis. All arithmetic runs through Decimal.js rather than native JavaScript floating point, which matters once currency is involved: a naive float calculation of 59.99 × 0.85 can pick up trailing binary rounding error, while the Decimal.js result is exact to the cent.

A worked example.

Frequently asked questions.

References& sources.

1. [1]Common Core State Standards for Mathematics, Grade 7, Ratios & Proportional Relationships, Standard 7.RP.A.3 — proportional relationships applied to multistep ratio and percent problems, explicitly including markups and markdowns.
2. [2]16 CFR Part 233.1 — Federal Trade Commission Guides Against Deceptive Pricing, governing when a former-price / percentage-off comparison is a lawful advertising claim.
3. [3]Common Core State Standards for Mathematics, Grade 6, Ratios & Proportional Relationships, Standard 6.RP.A.3(c) — finding a percent of a quantity, the foundational skill percent-off math builds on.
4. [4]NIST Guide to the SI, Special Publication 811, §7.10.2 — rules and conventions for expressing relative differences and ratios as dimensionless percentages.
5. [5]NIST Digital Library of Mathematical Functions, §4.2 — formal definitions of powers and multiplicative relationships underlying compounded-rate arithmetic such as stacked percentage discounts.