What is a percentage calculator?
A percentage calculator lets you find a percent of a number, what percent one number is of another, and percent increase or decrease—without juggling decimals by hand. Use it for grades, tips, discounts, tax rates, growth metrics, and budget splits. It pairs naturally with our tip calculator and discount calculator when you already know which flavor of percentage problem you are solving.
How to use this percentage calculator
- Pick the mode that matches your question — percent of a value, “A is what % of B?”, or change between two values.
- Enter numbers in consistent units — dollars with dollars, minutes with minutes—so the ratio stays meaningful.
- Read the result and sanity-check direction — increases should show positive % change; shrinkage should show negative.
- Round only at the end for reporting; keep extra digits while chaining steps to avoid compound rounding error.
Core formulas (reference)
Percent means “per hundred,” so divide by 100 when turning a human-readable percent into a decimal multiplier.
| You need | Formula |
|---|---|
| p% of a value V | V × (p ÷ 100) |
| A as % of B | (A ÷ B) × 100 |
| % change old → new | ((new − old) ÷ old) × 100 |
Worked example
Question: Your rent rose from $1,200 to $1,284. What is the increase? Change = (1284 − 1200) ÷ 1200 = 0.07 → 7%. Always divide by the original baseline unless a problem explicitly defines a different denominator (rare outside economics elasticity).
Decimal ↔ percent quick map
Restaurant tips and sales-tax lines are easier when you memorize a few decimal equivalents.
| Percent | Decimal |
|---|---|
| 15% | 0.15 |
| 18% | 0.18 |
| 20% | 0.20 |
| 8.25% | 0.0825 |
Percentages in school and work
Course syllabuses express weights as percents; analytics dashboards express conversion as percents—same math, different story. When a professor says the final is worth 40%, they mean 0.40 of your weighted average—use our GPA calculator for semester credit-weighted grades, or the weighted grade calculator for one class with multiple weighted components.
| Letter (typical) | 4.0 scale (simp.) | Notes |
|---|---|---|
| A (90–100%) | 4.0 (unweighted) | Excellent mastery |
| B (80–89%) | 3.0 | Above average |
| C (70–79%) | 2.0 | Satisfactory |
| D (60–69%) | 1.0 | Minimum passing |
| F (<60%) | 0.0 | No credit |
Tips for accurate percent math
Never average two percentages unless they share the same denominator or you explicitly weight them. Example: 10% of 100 plus 20% of 50 is not “15% overall” without defining the combined base.
Watch for “percentage points” versus “percent”—raising a rate from 3% to 4% is a one percentage point hike but roughly a 33% relative increase in the rate itself.
In spreadsheets, store decimals (0.18) in cells you multiply, and use percent display formats only for human reading to avoid double-dividing by 100.
More Q&A lives in the Frequently Asked Questions below (mirrors FAQ structured data).