Percentage Calculator
Calculate percentages, find what percent one number is of another, or compute percentage change.
Solve the three most common percentage problems instantly: finding a percentage of a number, working out what percent one number is of another, and calculating percentage change.
How Percent Calculator Works
To find X% of Y, the calculator multiplies: result = (X ÷ 100) × Y. For example, 20% of 150 is (20 ÷ 100) × 150 = 30.
To find what percent A is of B, it divides and multiplies by 100: percent = (A ÷ B) × 100. For example, 30 is what percent of 150? (30 ÷ 150) × 100 = 20%.
To find percentage change between an old and new value, it calculates: change = ((new − old) ÷ old) × 100. A positive result is a percentage increase; a negative result is a percentage decrease.
See It In Action
Who Uses Percent Calculator and Why
- Figuring out a sale discount amount and final price from a percentage-off tag.
- Working out what percent a test score or survey response represents of the total.
- Calculating the percentage change in a price, salary, or measurement between two points in time.
- Determining the target value after a planned percentage increase, like a budget or rent adjustment.
Mistakes to Avoid
- Assuming a percentage decrease and an equal percentage increase cancel out — a 20% decrease from 150 lands at 120, but reversing it needs a 25% increase, not 20%, because each percentage is calculated against a different base value.
- Confusing percentage points with percent — a rate moving from 10% to 15% is a 5 percentage point change, but a 50% relative increase, and these numbers get mixed up constantly.
- Using the new value as the base in a percentage change calculation instead of the old (starting) value, which the formula specifically requires.
Tips for Best Results
- Remember percentage change is always calculated relative to the original (old) value, never the new one — this explains why increases and decreases of the same percentage don't mirror each other.
- To find a target value after a percentage increase, multiply the original number by (1 + percent ÷ 100) rather than calculating the increase amount separately.
Fixing Common Problems
Reversing a percentage decrease with the same percentage increase doesn't get me back to my starting value. — This is expected — percentage change is calculated relative to a different base each time. Use the percentage change mode directly on the two actual values instead of assuming symmetry.
Terms Explained
Percentage point: The raw difference between two percentages (e.g., 15% − 10% = 5 percentage points), distinct from the relative percent change between them.
Base value: The starting or reference number a percentage is calculated against — critical to get right in percentage change problems.