Discount Calculator
Enter the original price and a discount percentage to get the final price and the amount saved.
輸入資料
計算結果
重點速覽：Amount saved = original price x discount% / 100; final price = original price - amount saved. Note Hong Kong's 'X 折' means paying X ty of the original (e.g. '七五折' = pay 75% = 25% off), the opposite direction from 'percent off'. This calculator takes the percentage OFF, so '七五折' = enter 25. WARNING: Single discount only; for stacked discounts use the double-discount calculator and add tax separately.
計算公式
節省金額 = 原價 × 折扣% ÷ 100。
折後價 = 原價 − 節省金額。
$$節省金額：$Saved = Price\times\dfrac{Discount\%}{100}$$$$$折後價：$Final = Price - Saved$$$$$示例：$100\times\dfrac{25\%}{100}=25$,折後 $75$$$使用說明
- Enter the original price before discount.
- Enter the percentage off (for '七五折' enter 25).
- View the final price and the amount saved.
不同原價與折扣百分比下的節省金額與折後價
| 原價 (HK$) | 折扣 (% off) | 節省金額 (HK$) | 折後價 (HK$) |
|---|---|---|---|
| 100 | 25% | 25 | 75 |
| 1,200 | 30% | 360 | 840 |
| 899 | 10% | 89.9 | 809.1 |
理財情境案例
案例一：計算折後價與節省金額
某商品原價 HK$1,200，商店標示『七折』(即 30% off)。
節省金額 = 1,200 × 30% = HK$360；折後價 = 1,200 − 360 = HK$840。
解讀：這件原價 HK$1,200 的商品，七折後實付 HK$840，省下 HK$360。購物時搞清楚『折扣百分比』與『折後實付』,才能快速判斷是否划算，也方便比較不同商店的優惠。
案例二：兩重折扣不能直接相加
某原價 HK$1,000 的商品，先享『七折』(30% off),結帳時再用『九折券』(額外 10% off)。很多人以為總折扣是 30% + 10% = 40% off，實付 HK$600——這是錯的。
正確算法是逐次相乘：1,000 × 0.7 × 0.9 = HK$630。等效總折扣只有 37% off (省 HK$370),而非 40%。
解讀：多重折扣是『在上一次折後價的基礎上再打折』,所以要連乘、不能相加。先 30% off 後只剩 700，再打 9 折 (乘 0.9) 得 630，實際只省了 37%。這是商店促銷常見的『數字陷阱』——『再減 10%』聽起來很多，但它是對已折扣的價格再減，效果比想像中小。遇到疊加優惠時，逐步計算折後價才不會被誤導。本計算器一次算單一折扣，多重折扣請把折後價再輸入一次計算。
常見問題
What should I enter for '七五折'?
Hong Kong '七五折' means paying 75% of the original price, i.e. a 25% reduction. This calculator takes the percentage OFF, so enter 25. '八折' (pay 80%) = enter 20, and so on.
What is the difference between discount and markup?
A discount reduces a selling price; a markup adds to a cost. Their percentage bases differ, so they are not directly interchangeable. Use the markup calculator for cost-based pricing.
Can two discount coupons be added together?
If one discount applies to the already-discounted price, it is a double discount and does not equal the sum of the percentages. Use the double-discount calculator for the correct final price and equivalent rate.
Why does 'Hong Kong ty off' use a different input?
In Hong Kong, 'X 折' expresses the share you PAY (X ty), while 'percent off' expresses the share you SAVE. They are complementary (sum to 100%): discount % off = 100% - (X x 10%). '七五折' -> 100% - 75% = 25% off. Enter the 25, not 75. If you entered 75 by mistake, the tool would compute 75% off (pay 25%), which is wrong.
相關工具
參考資料
內容審核：香港計算器財經團隊。計算邏輯與公式參考香港金融管理局（HKMA）及投資者及理財教育委員會（IFEC）之個人理財計算指引，結果僅供參考，實際以相關機構公佈為準。