この計算機の使い方
What a discount calculator actually does
The discount calculator handles the arithmetic that comes up every time something goes on sale: what does this price become after a percentage discount, and how much do I actually save? You type two numbers — the original price and a discount percentage between 0 and 100 — and the calculator returns the exact amount you save and the final price, both rounded only for display. It is the same calculation a cashier performs at the register, which is exactly why you should not do it in your head mid-negotiation: a 33.3% discount on $99.99 is the kind of figure that invites rounding slips, and the calculator keeps every decimal until the moment results are shown. The tool is deliberately narrow: one price, one discount, one clear answer — which keeps the math trustworthy instead of buried in a spreadsheet of assumptions.
Use it when you set sale prices for your own products, when a supplier quotes a percentage off and you want to know what the invoice will actually show, or when you are comparing two offers — a 40% discount on one item and a 25% discount on another are not comparable by percentage alone, because each percentage applies to a different base price. The calculator works for any single price-and-discount pair: a jacket, a service retainer, a monthly subscription. It deliberately does not handle stacked discounts — a second discount applied to the first result — nor tiered quantity pricing nor sales tax. Those are different jobs with different models; this tool covers one question well rather than several questions badly, and its results stay honest because its scope is explicit.
Entering original price and discount percentage
Original price is the price before the discount — the sticker price, the list price, or the price you were going to charge before the promotion. Type it in dollars with cents if you like; the field accepts dots or commas as decimal separators and strips spaces, so 99.99, 99,99, and 1 299.00 all parse to the same value. The label matters: the calculation starts from this number, so enter the price the customer would have paid without the promotion, not the already-reduced price. A 25% discount applied to an already-discounted price saves less than 25% of the original — that is the stacked-discount trap in miniature — and starting from the wrong base is the single most common way people misstate their savings. When you set your own sale, the original price is also the anchor customers compare against, so entering it accurately keeps your marketing copy honest.
Discount percentage is a number between 0 and 100, entered as the percentage itself — type 25 for a 25% discount, not 0.25. A field expecting a percentage reads 0.25 as a quarter of one percent, which turns a $30 saving into thirty cents on a $120 item. Values above 100 are rejected, because a discount above 100% would mean the seller pays the buyer; the calculator explains the allowed range instead of returning a nonsense negative price. Zero is allowed and useful: a 0% discount simply returns the original price, which is a quick way to confirm the tool is reading your entry the way you intended. For odd percentages like 33.3 or 12.5, type them exactly — decimal precision is preserved through the whole calculation. The hint under the field — Between 0 and 100 — says it plainly: the range is part of the definition of a discount, not an arbitrary limit.
Reading the savings and the final price
You save is the discount amount — the original price multiplied by the discount percentage — shown as currency with two decimals. Final price is the original price minus that amount, also two decimals, and the two always agree because they come from a single calculation: the discount is computed in full decimal precision and only the displayed values are rounded. So a 33.3% discount on $99.99 shows $33.30 saved and a final price of $66.69, precise to the cent with no drift from intermediate rounding. Everything outside those two numbers — tax, shipping, handling fees — is deliberately out of scope, and the note under the calculator says so, which is what keeps the result unambiguous when you rely on it. If the two figures ever look inconsistent with the percentage you entered, check the percentage field first: a typo of 15 instead of 1.5 changes a $120 item by more than $16.
Check two things when you read the results. First, whether the final price is what you actually want to charge: if the sale price no longer covers your cost plus a working margin, the discount is too deep — lower the percentage and re-run until the final price meets your floor. Second, whether the percentage matches the deal you agreed to: a supplier who quotes 15% off a $2,400 machine but prices the invoice as if it were 10% is easy to catch when the exact final price is on screen — $2,040 versus $2,160 is a $120 difference that the reverse arithmetic in the Formulas section exposes. And remember the results are pre-tax: include tax in the entered price if you need the number a customer actually hands over. Rounding is half away from zero at the display step, so the cents you see are the cents a receipt would show.
結果はどうやって計算されるの？
セール価格設定：120.00 の 25% オフ
$120 のジャケットが25%オフのセールになります。割引額は 120 × 0.25 = $30 なので、最終価格は $90 です。この $90 にさらに25%の割引を適用しても、値引かれるのは $22.50 だけです。連続する割引は足し算になりません。
入力と出力の例 | 入力 | 値 |
| 元の価格 | 120.00 |
| 割引率 | 25 |
| 結果 | 割引額 $30.00 · 最終価格 $90.00 |
Odd discount, exact answer: 33.3% off 99.99
A shopkeeper prices a lamp at $99.99 and runs a 33.3% off sale to clear the last of the season's stock. The discount amount is 99.99 × 33.3 / 100 = 33.29667, which rounds to $33.30, and the final price is 99.99 − 33.29667 = 66.69333, which rounds to $66.69. The odd percentage makes the point: because the calculator multiplies in full decimal precision and rounds only what it displays, the answer lands on exact cents instead of a guess. It is like a cashier who works out change to the cent rather than rounding the bill up to the nearest dollar — the customer gets the honest figure and the till matches at closing. A mental shortcut works for friendly percentages, but 33.3% on 99.99 is exactly the case where shortcuts drift: estimating one-third gives $66.66, and the true figure of $66.69 is three cents off per item — a real difference when you sell dozens. Compare it with the $90 jacket example: the arithmetic has the same shape, only the numbers change. To see the precision matter, run 25% off $99.99: the discount is 24.9975, displayed as $25.00, and the final price 74.9925, displayed as $74.99 — a case where the penny is earned by the decimal arithmetic, not by rounding up. For the shopkeeper, the distinction between $66.69 and a rounded $66.70 on every lamp matters twice: once at the register, where the till must balance, and once in the promotion's advertising, where a stated price is a promise. Enter the values exactly as typed here — price 99.99 and discount 33.3 — and the result row shows You save $33.30 and Final price $66.69.
入力と出力の例 | 入力 | 値 |
| 元の価格 | 99.99 |
| 割引率 | 33.3 |
| 結果 | You save $33.30 · final price $66.69 |
Checking a supplier quote: 15% off 2,400.00
A supplier quotes you $2,400 for a commercial espresso machine, then offers 15% off for paying within ten days. The discount amount is 2,400 × 0.15 = $360, and the final price is 2,400 − 360 = $2,040. Run the same number from the other side when you haggle: if you counter at $2,000 and the supplier accepts, the real discount was (2,400 − 2,000) / 2,400 × 100 = 16.7%, not the 15% you started from — every percentage point on a $2,400 base is $24 of real money. Haggling here works like bartering at a market stall: the sticker price is the starting point, and the discount is a fixed share of that starting point, so a generous-sounding percentage on a big base is worth more than a headline percentage on a small one. Use the calculator to translate each offer into the only two numbers that matter: the dollars you save and the dollars you pay. Now check the supplier's math the other way around: a quote of 15% that arrives as $2,160 instead of $2,040 is really only a 10% discount — the (original − final) / original formula from the Formulas section catches invoice arithmetic that a quick glance misses. The same pattern repeats in everyday shopping: a store that marks $80 shoes down to $64 has applied exactly 20%, while a store that marks $120 jackets down to $96 has also applied 20% — equal percentages, unequal dollars, and only the calculator shows both at once. Type 2400.00 as the original price and 15 as the discount percentage, and the result row reads: You save $360.00, final price $2,040.00. Keep that screen open while you negotiate — it turns a percentage conversation into a dollar conversation, which is where the real bargaining happens.
入力と出力の例 | 入力 | 値 |
| 元の価格 | 2400.00 |
| 割引率 | 15 |
| 結果 | You save $360.00 · final price $2,040.00 |
よくある質問
割引を重ねると足し算になりますか？
いいえ。20%割引の後にさらに20%割引を適用すると、すでに割引された価格の20%が引かれるため、合計の割引は40%ではなく36%になります。この計算ツールの逆算モードで元の価格と最終価格を入力すると、合計の割引率が正確に表示されます。
割引が100%を超えることはありますか？
通常の価格設定ではありえません。100%を超える割引は、売り手が買い手にお金を払うことを意味します。計算ツールは0〜100%の範囲外の割引率を拒否し、その範囲を説明します。
割引後の価格は、その価格での粗利率と同じですか？
いいえ。$120 の25%割引は $90 になります。この商品の原価が $60 なら、販売価格に対する粗利率は33.3%ですが、原価に対する25%のマークアップは $75 です。割引は価格から引かれ、粗利率は最終価格に対して測られます。それぞれ粗利率計算ツールとマークアップ計算ツールをご覧ください。
Does the calculator include sales tax?
No. The final price is pre-tax unless you include tax in the entered price. If you need the total a customer pays, add the tax to the original price before entering it, or compute tax on the final price yourself. Tax is left out deliberately: rates vary by state and product category, so including them would make every result region-specific. The note under the calculator says the same thing, so the numbers are unambiguous — You save and Final price always refer to the pre-tax figures.
What if I only know the original and final prices?
Enter the original price and work out the percentage with the formula in the Formulas section: (original − final) / original × 100. For example, an item that was $120 and sold for $90 is a 25% discount: (120 − 90) / 120 × 100 = 25. The same check catches misquotes: a supplier who says 15% off a $2,400 machine but invoices $2,160 has really given 10%. This calculator takes the percentage directly, so it covers the pricing direction; the formula covers the verifying direction.
Is the percentage discount the same as the percentage I add back later?
No, and this is a common pricing trap. If an item drops from $100 to $75, the discount is 25%. Getting back to $100 from $75 is not a 25% increase — 25% of $75 is only $18.75, reaching $93.75 — you need a 33.3% increase, because the discount was taken off the higher base and the increase is applied to the lower one. The discount calculator shows the downward side of that pair; the markup and margin tools cover the upward side.