Percentage Calculator
Three percentage questions, each with its own answer
すべての処理はブラウザ内で完結します。データが端末外に送信されることはありません。
関連ツール
使い方
Most percentage confusion comes from conflating distinct questions. Each mode here corresponds to one, with fields labelled for that question rather than as generic A and B.
Choose the question you are asking
"X% of Y" finds a portion of a total. "X is what % of Y" turns two numbers into a proportion. "% change" compares a before and an after value.
Enter the two values
The field labels change with the mode, so the first field always means what its label says — a percentage in the first mode, a raw value in the others.
Read the result
The first mode returns a plain number; the other two return percentages. Percentage change can be negative, which indicates a decrease.
Watch for a zero baseline
Percentage change from zero is mathematically undefined — there is no baseline to compare against — so the calculator says so rather than showing a misleading infinity.
使用例
Calculating a tip
For a 15% tip on an 86 bill, use "X% of Y" with 15 and 86, giving 12.90. The total to leave is 98.90.
Measuring growth
Revenue rising from 42,000 to 58,000 is a 38.1% increase — use "% change" with 42000 as the from value and 58000 as the to value. Falling back to 42,000 later would be a 27.6% decrease, not 38.1%, because the baseline is now larger.
このツールについて
Solve the three percentage problems people actually run into: what is X percent of Y, X is what percent of Y, and the percentage change between two values. Each mode is labelled in plain language so you never have to remember which number goes where. Results update as you type.