Compute “what is X% of Y”, reverse percentages, and percentage change for shopping, grades, and business checks.
To take 20% off a $80 price, compute 20% of 80 (=16) and subtract, or compute 80 × (1 − 0.20). The decrease modes on this page mirror that workflow.
Percentage change is relative to the starting value ((new − old) / old). Percentage points measure absolute distance between two percents (for example 10% to 12% is 2 points).
No. Figures are arithmetic helpers for estimates and study — not tax, investment, or lending advice.