パーセント変化率計算機
2つの値の間のパーセント変化率を計算します。
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Calculating Percentage Increase and Decrease
概要
Percentage change measures how much a value has grown or shrunk relative to its starting point — essential for tracking prices, metrics, and results. This calculator finds the percentage increase or decrease between two numbers instantly in your browser.
使い方（ステップ）
- 1
Enter the original value
The starting (old) number.
- 2
Enter the new value
The number you are comparing against the original.
- 3
Read the percentage change
A positive result is an increase, negative is a decrease.
仕組み
Percentage change = ((new value − old value) ÷ old value) × 100. A positive result is an increase, a negative one a decrease. The key is that the change is always measured against the original (old) value, which is why a rise from 50 to 100 is a 100% increase, but a fall from 100 to 50 is only a 50% decrease — the base is different each way.
こんなときに使う
Tracking a price rise or drop. Measuring growth in followers, sales, or traffic. Comparing this period's figure against last period's.
よくある質問
Because percentage change is measured against the starting value. 50 to 100 is +100% (base 50), but 100 to 50 is −50% (base 100).