％ 百分比计算器Percentage Calculator
在线百分比计算：求某数的百分之几、占比多少、涨跌幅百分比。Calculate X% of Y, what percent X is of Y, and percentage change.
使用说明与常见问题How-to & FAQ
「百分比计算器」是什么？What is the Percentage Calculator?
在线百分比计算：求某数的百分之几、占比多少、涨跌幅百分比。Calculate X% of Y, what percent X is of Y, and percentage change.
如何使用「百分比计算器」？How do I use the Percentage Calculator?
在「百分比计算器」中，在上方填写或选择所需内容，结果会实时显示在下方；所有处理都在浏览器本地完成。In the Percentage Calculator: Fill in or choose the options above and the result appears below instantly; everything runs locally in your browser.
涨幅怎么算？How is percentage change calculated?
涨跌幅 =（新值 − 原值）÷ |原值| × 100%。原值为负数时用绝对值作分母，这样数值变大总是显示为正增长；原值为 0 时无法计算。Change = (new − old) ÷ |old| × 100%. Using the absolute value means an increase is always shown as positive even when the start is negative; it is undefined when the start is 0.
计算精度如何？How precise are the results?
「百分比计算器」使用 JavaScript 双精度浮点数（约 15–16 位有效数字）；极大或极小的数值可能存在精度误差。The Percentage Calculator uses double-precision floating point (about 15–16 significant digits); very large or very small values may lose precision.
「百分比计算器」免费吗？需要注册吗？Is the Percentage Calculator free? Do I need an account?
「百分比计算器」完全免费，无需注册或安装，打开网页即可使用，手机和电脑都能用；输入的内容只在你的浏览器本地处理。The Percentage Calculator is completely free with no sign-up or install and works on phones and desktops; what you enter is processed only in your browser.