DISCOUNT
Discounts & coupons, to the last cent.
Four scenarios: percentage off, spend X get Y off, a discount stacked with a threshold, and the equivalent rate of chained discounts; plus reverse-engineering the original price from the sale price. All amounts are computed in integer cents, so no floating point drift.
Everything runs locally in your browser
How to use
Pick a scenario and fill the amounts: "percentage off" takes the original price and rate (80 means 20% off); "spend X get Y off" takes the price, the threshold and the amount off per threshold (300 / 50 means every 300 saves 50, and the number of times is counted for you); "discount + threshold" applies the discount first, then the threshold; "chained discounts" takes two rates and multiplies them (80% then 90% = 72%, not 17%); "reverse" takes the final price and the rate to recover the original. Results can be copied with one click.
Common questions
What is 20% off followed by 10% off?
72%, i.e. 7.2 off. Discounts multiply, they do not add: 0.8 × 0.9 = 0.72. Subtracting 0.8 − 0.1 = 0.7 would treat them as stacked cash discounts — only flat reductions (spend-and-save coupons) can simply be added.
How do threshold discounts actually work?
Usually per threshold: "spend 300 save 50" means 599 saves only 50 (599 is under 600) while 600 saves 100; some promotions apply it once regardless. This page counts the threshold multiples explicitly so you can compare with the promotion rules.
Discount first or threshold first?
Discount first is usually better: it lowers the price so the threshold is easier to reach. The "discount + threshold" scenario follows that order and shows the intermediate price. If the promotion states the opposite order, swap the two steps.
Is any data uploaded?
No. All computing runs locally in the browser.
示例与注意事项Example & notes
一个例子A worked example
一件 299 元的衣服打八折：填原价 299、折扣力度 80，立刻得到应付 239.20、优惠 59.80、优惠率 20%，并注明「相当于打 8 折」。A 299 yuan item at 20% off: enter 299 and 80 and you get 239.20 to pay, 59.80 saved, 20% off — annotated as "8 zhe".
注意事项Things to watch
- 金额按「分」做整数运算，299 × 0.8 这类计算不会出现 239.199999 之类的浮点误差。Amounts are computed in integer cents, so 299 × 0.8 never shows float noise like 239.199999.
- 满减按「每满可减一次」计算：满 300 减 50 时 599 元只减一次、600 元减两次；活动若写明不区分倍数，以活动规则为准。Thresholds apply per multiple: with "spend 300 save 50", 599 saves 50 once while 600 saves it twice; if the promotion says otherwise, follow the promotion rules.
- 多次打折是连乘而不是相加：八折后再九折 = 72%，不是 70% 也不是 17%。Chained discounts multiply: 80% then 90% = 72% — not 70% and not 17%.
相关问答More Q&A
怎么判断哪个优惠方案更划算？How do I compare two promotions?
把两种方案都换算成「最终应付金额」再比：先折后减一般更划算，因为打折先压低了价格，满减门槛更容易达到。本页的「折扣 + 满减」场景按此顺序计算并显示中间价，交换两步即可算另一种顺序。Convert both to a final amount and compare: discount-then-threshold is usually better because the lower price reaches the threshold more easily. The "discount + threshold" scenario follows that order and shows the intermediate price; swap the two steps for the other order.
「反推原价」有什么用？What is the reverse mode for?
看到折后价想比较是否真的便宜时用：先按折扣反推原价，再拿原价与同类商品比价，能避免被「先涨后折」骗到——反推出的原价往往比原价高，说明折扣是虚的。Use it when you see a sale price and want to judge whether it is genuinely cheap: derive the original price from the discount, then compare that with similar products — a high derived original price exposes a fake discount.