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Percentage Formula Reference
A compact reference for percent-of, what-percent, percentage change, and reverse-percentage formulas.
Core percentage formulas
Percent of a value: result = base × percentage ÷ 100.
What percent is A of B: percentage = A ÷ B × 100.
Percentage change: (new − old) ÷ |old| × 100.
Increase a value by p%: new = original × (1 + p ÷ 100).
Decrease a value by p%: new = original × (1 − p ÷ 100).
Reverse an increase: original = final ÷ (1 + p ÷ 100).
Reverse a decrease: original = final ÷ (1 − p ÷ 100), when the divisor is not zero.
How this resource works
These identities follow directly from the definition of percentage as a quantity per hundred.