Practical guide

How to Calculate Percentages

Simple formulas and examples to calculate percentages quickly.

Quick Answer

To find X% of a number, multiply the number by X and divide by 100. To find what percent A is of B, divide A by B and multiply by 100.

Step-by-Step Method

Identify the base value (the whole amount you are comparing against).
Choose the percentage you need: part-of-whole, increase, or decrease.
Apply the formula: part = base × percent ÷ 100, then add or subtract for change scenarios.
Round only at the final step to avoid compounding rounding errors.

Worked Example

What is 15% of 240? Calculation: 240 × 15 ÷ 100 = 36. If you need a 15% increase, the new value is 240 + 36 = 276.

Detailed Explanation

Almost every percentage error traces back to using the wrong base. The question is always "percent of what?", and the answer is rarely the number closest to hand. Calculating a markup against the sale price instead of the cost price, or a discount against the already-discounted figure, produces a number that is arithmetically correct and commercially wrong. Before dividing, name the base out loud — it catches most mistakes before they reach an invoice.

Percentage changes are not symmetric, which surprises people repeatedly. A value that falls 50% needs to rise 100% just to return to where it started, because the increase is measured against the smaller number. This is why a portfolio down 20% one year and up 20% the next is not back to even — it is down 4%. Whenever you compute a change, divide by the original value, not the new one: a drop from 80 to 60 is a 25% decrease, not 33%.

Two further traps are worth knowing. Successive percentages do not add: a 10% discount followed by another 10% is 19% off, not 20%, because the second applies to the reduced price. And percentage points are not percent — an interest rate moving from 5% to 8% has risen 3 percentage points but 60% in relative terms, and financial reporting uses both. When precision matters, run the scenarios side by side in our percentage calculator before committing numbers to a report.

Use the Calculator

Run your real values in the interactive tool and review assumptions before taking action.

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FAQ

How do I calculate percentage increase?

Subtract the old value from the new value, divide by the old value, and multiply by 100.

What is the difference between percentage points and percent change?

Percentage points measure absolute difference (5% to 8% = 3 points). Percent change measures relative growth (5% to 8% = 60% increase).

When should I round percentage results?

Keep full precision during intermediate steps and round only the final displayed value.