WebToolArcFormula and interpretation
result = base × percent ÷ 100.
A percentage is a rate per 100; 20% means 0.20 as a decimal multiplier.
Percentage formulas at a glance
Pick the form that matches the question. The calculator keeps the reference value explicit because percentage change and percentage difference do not use the same denominator.
percent of = value × percent ÷ 100
what percent = part ÷ whole × 100
percent change = (new − original) ÷ original × 100
what percent = part ÷ whole × 100
percent change = (new − original) ÷ original × 100
Example
For 15% of 200, convert 15% to 0.15 and multiply: 200 × 0.15 = 30. For a move from 80 to 100, the change is 20 ÷ 80 × 100 = 25%.