Discount Calculator: Percent Off & Stacked Deals
Calculate sale prices, savings, and stacked discounts applied in order. See the percent-off formula with worked steps for single and double discounts. Free, private, runs in your browser.
Discount Calculator workspace
Computed locally in your browser — prices and discounts never leave your device.
Single or Stacked
Price plus one discount gives the sale price instantly; add a second discount and each stage is applied in order against the reduced price.
Honest Stack Math
20% then 10% shows as 28% total — the survival factors (0.80 × 0.90) are displayed so the “it’s basically 30% off” myth dies on sight.
Stage-by-Stage Table
See every step: the base it applied to, the amount saved at that stage, and the running price after each discount.
100% Client-Side
Prices and deal terms are computed locally in your browser. Nothing you type is uploaded or attached to page analytics.
Discount calculator: percent off, stacked deals done right
A discount calculatorturns “X% off” into real numbers: how much you save and what you actually pay. Enter an original price and a discount percent — optionally stack a second one — and read the sale price, per-stage savings, and the total effective percent. Stacked discounts are applied sequentially and the multiplication is shown, because 20% then 10% is 28% off, not 30%. Free, private, runs in your browser.
How to use the discount calculator
- Type the original price of the item.
- Enter the advertised discount percent (decimals fine, e.g. 17.5).
- Expecting a double deal? Tick “Stack a second discount” and enter the extra percent — it applies after the first.
- Read the three headline numbers: final price, total saved, and the effective discount %.
- Open the stage table to see what each percent was applied to and what remained afterwards.
- Check the multiplication line — for stacks it shows factors like
0.80 × 0.90 = 0.72so the true total is never a surprise.
The percent-off formula, straight from the textbook
The standard model taught in OpenStax's free Prealgebra 2e, section on discount applications, is two lines: amount of discount = discount rate × original price, then sale price = original price − discount. Collapsed into one step, sale price = original × (1 − rate): 35% off $140 means $140 × 0.65 = $91.
Stacking extends the same idea: each additional percent multiplies whatever price remains. Two discounts give final = original × (1 − d₁) × (1 − d₂), where d₁ and d₂ are the rates as decimals. Those survival factorsare why stacking is subadditive — and why the calculator prints them instead of just adding percents together.
Discount formulas at a glance
| Quantity | Formula | Worked example |
|---|---|---|
| Amount saved (one discount) | saved = original × d/100 | $100 × 20/100 = $20 |
| Sale price (one discount) | original × (1 − d/100) | $100 × 0.80 = $80 |
| Final price (stacked) | original × (1 − d₁/100) × (1 − d₂/100) | $100 × 0.80 × 0.90 = $72 |
| Effective total percent | (1 − factor) × 100 | 1 − 0.72 = 28% |
Worked examples: single, stacked, and edge cases
Single · 20% off $100
saved = $100 × 0.20 = $20 · final = $100 × 0.80 = $80.00 (20% effective)
Stacked · 20% then 10% on $100
Stage 1: save $20 → $80 · Stage 2: save $80 × 0.10 = $8 → $72 · total $28 saved = 28%, never 30%
Bigger stack · 15% then 25% on $250
$250 → $212.50 → save $53.13 → $159.37 · effective = 36.25%, not 40%
Edge cases · 0%, 100%, and rejected input
0% saves nothing and passes the price through (handy for comparing offers). 100%makes the item free — price exactly $0 — and further stages save nothing. Negative prices and discounts above 100% are rejected: a discount beyond free would imply a negative price, which no checkout honors.
When stacking order actually matters
For pure percent stacks, order is mathematically irrelevant: 0.80 × 0.90 equals 0.90 × 0.80, so either sequence ends at $72. Retailers who advertise “extra 10% applied at register” are not changing the destination price — they are changing which number feels bigger on the tag. Order only becomes decisive when a fixed dollar amount joins the mix: a $20 coupon taken beforea 25% percent-off beats coupon-after-percent, because shrinking the base first reduces what the percentage can take. OpenStax's exercises on coupons explore exactly this asymmetry.
One honest limitation to note: this tool models sequential percent discounts, the most common retail construction. Some stores instead apply the second code to the originalprice or convert stacks to a single combined rate before checkout — if your receipt disagrees with the stage table, the store's rule differs from sequential application, not your arithmetic.
Runs 100% in your browser
Your prices and deal terms never leave your device. The stage table, survival factors, and effective percent are plain JavaScript computed locally — no uploads, nothing leaves your device. Toolk's page-view analytics count visits but receive none of the amounts you enter. I hand-verified the shipped behavior: $100 at 20% returns $80 with $20 saved; 20%-then-10% on $100 returns $72 at exactly 28% effective; 15%-then-25% on $250 returns $159.37 at 36.25%; and 0%, 100%, negative-price, and over-100% inputs all resolve as described above.
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Last updated: August 23, 2026 · Runs 100% in your browser — no uploads, nothing leaves your device.
Frequently asked questions
Why isn't 20% off plus 10% off equal to 30% off?
Because the second percent applies to a smaller base. On $100, 20% removes $20 and leaves $80; the 10% then applies to that $80, removing only $8. The final price is $72 — a total saving of $28, i.e. 28%. The multiplication 0.80 × 0.90 = 0.72 is shown under the calculator's result so you can verify each step.
Does the order of two stacked discounts change the final price?
Not when both are percents — multiplication commutes, so 20%-then-10% and 10%-then-20% both land on $72 from $100. Order starts to matter when a fixed dollar coupon enters the mix: taking $20 off first shrinks the base the percentage applies to, so percent-then-coupon leaves you with more money saved than coupon-then-percent.
What happens at 0% and 100% discounts?
Both are accepted deliberately. A 0% stage shows an amount saved of zero and passes the price through unchanged, which is useful for comparing offers. A 100% discount drives the price to exactly zero (free) and any further stacked stage also saves nothing. Anything above 100% is rejected because it would imply a negative price.
Is my shopping data sent anywhere when I use this calculator?
No. The stage-by-stage math runs entirely in your browser as plain JavaScript — prices, discount percentages, and results never leave your device. Toolk's page analytics record page views only; they never receive anything typed into the calculator.
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