Free Percentage Calculator — Discounts, Tips & Percent Change
Percentages hide in plain sight: store discounts, restaurant tips, salary raises, tax rates, and grade curves. This free calculator answers the three questions people actually ask — what is X% of Y, X is what percent of Y, and what is the percent change from Y to X — plus a dedicated tip-and-split tool for restaurant bills.
How to Calculate Any Percentage
- Enter both numbers — the interface labels them X and Y to match each formula.
- Pick the question — "X% of Y" for discounts and portions, "X is what % of Y" for grades and shares, "% change" for growth and price moves.
- Split the bill below — set the tip percent and headcount for per-person totals instantly.
The Three Formulas, Demystified
X% of Y multiplies: 20% of 150 = 0.20 × 150 = 30. X is what % of Y divides: 30 is (30 ÷ 150) × 100 = 20% of 150. Percent change divides the difference by the starting value: from 120 to 150 is (150−120) ÷ 120 = +25%. The classic trap is percentage points versus percent: a rate rising from 10% to 12% gained two points but grew twenty percent — very different claims.
How do I calculate a discount quickly?
Subtract the discount from 100 and multiply: 30% off $80 means paying 70%, so 0.70 × 80 = $56. The "X% of Y" mode does exactly this step.
What is a good restaurant tip?
15–20% is standard in the US for table service, 10% for casual counter spots. The splitter divides the tipped total evenly — rounding each share up to the nearest dollar keeps math painless.
Why do percent changes mislead?
Because the base shifts: +50% then −50% does not return to start (150 → 75 on a 100 base). Always note which value is the denominator.
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