Percentage Calculator
Calculate percentages, change, and differences
Percentage Calculator — what it does
Three percentage calculations in one place: what X percent of Y is, what percentage X is of Y, and the percentage change between two values. Between them they cover almost every percentage question that comes up in ordinary work, without the wrong-way-round errors that doing it in your head invites.
When this tool helps
- Working out a tip, a commission or a share of a total.
- Expressing a result as a percentage of a target for a report.
- Calculating growth or decline between two periods.
How to use it
- Choose the calculation you need.
- Enter value X and value Y.
- Calculate.
- Read the result.
Accuracy, limits, and good practice
- Percentage change is not symmetric: a fall from 100 to 50 is minus 50 percent, but recovering from 50 to 100 is plus 100 percent.
- Successive percentages multiply rather than add — up 10 percent then down 10 percent leaves you at 99, not back where you started.
- Keep percentage points and percent distinct: moving from 20 to 25 percent is five percentage points, and a 25 percent increase.
Frequently asked questions
How do I reverse a percentage increase?
Divide by one plus the rate. A price of 120 after a 20 percent increase started at 100, not at 96.
Which of the three calculations do I want?
"What is X% of Y" for a share, "X is what % of Y" for a proportion, and percentage change for growth between two figures.
Can it handle a decrease?
Yes, percentage change returns a negative value when the second figure is lower than the first.
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Everything above runs inside this page. Percentage Calculator needs no account, no upload, and no server round trip — close the tab and nothing is left behind.
百分比計算器能做什麼
三種百分比計算集中在一處：Y 的 X% 是多少、X 佔 Y 的百分之幾，以及兩個數值之間的百分比變化。這三種涵蓋了日常工作中幾乎所有的百分比問題，也避開了心算最容易犯的方向錯誤。
什麼時候用得上
- 計算小費、佣金或某項佔總額的份額。
- 在報告中把結果表達成目標達成率。
- 計算兩個期間之間的成長或衰退。
使用步驟
- 選擇需要的計算方式。
- 輸入數值 X 與數值 Y。
- 執行計算。
- 查看結果。
精確度、限制與實務建議
- 百分比變化不對稱：從 100 掉到 50 是 −50%，但從 50 回到 100 是 +100%。
- 連續百分比是相乘不是相加——先漲 10% 再跌 10%，結果是 99 而不是回到原點。
- 要區分「百分點」與「百分比」：從 20% 到 25% 是五個百分點，同時也是增加了 25%。
常見問題
怎麼反推漲價前的數字？
除以（1 + 漲幅）。漲 20% 後是 120 的價格，原本是 100，而不是 96。
三種計算我該用哪一個？
算份額用「Y 的 X% 是多少」，算佔比用「X 佔 Y 的百分之幾」，兩數之間的成長用百分比變化。
可以算下降嗎？
可以，第二個數字較低時，百分比變化會回傳負值。
本站相關工具
- JSON 轉 CSV — 將 JSON 物件陣列轉換成 CSV
- 插入 PDF 空白頁 — 在指定位置插入空白頁面
- PDF 頁面反向排序 — 將 PDF 頁面順序完整反轉
以上步驟全部在這個頁面內完成，百分比計算器 不需要註冊、不上傳檔案、也不經過伺服器，關閉分頁後不會留下任何資料。