To calculate a percentage of a number, multiply the number by the percentage (expressed as a decimal). For example, to find 15% of 200: convert 15% to 0.15, then multiply 200 × 0.15 = 30. The formula is: Result = (Percentage ÷ 100) × Number. Our Find % tab does this instantly.

The percentage increase formula is: New Value = Original × (1 + Percentage ÷ 100). For instance, increasing 200 by 15%: 200 × (1 + 0.15) = 200 × 1.15 = 230. The increase amount alone is 200 × 0.15 = 30. Use the Increase tab to compute this automatically.

The percentage decrease formula is: New Value = Original × (1 − Percentage ÷ 100). For example, decreasing 200 by 15%: 200 × (1 − 0.15) = 200 × 0.85 = 170. The decrease amount is 200 × 0.15 = 30. This is commonly used for calculating discounts and sale prices.

The percentage change formula is: Change = ((New Value − Old Value) ÷ |Old Value|) × 100. If a stock rises from $200 to $230, the change is ((230 − 200) ÷ 200) × 100 = +15%. A positive result indicates an increase; a negative result indicates a decrease. Use the % Change tab for instant results.

To find what percent X is of Y, use: Percent = (X ÷ Y) × 100. For example, 30 is what percent of 200? (30 ÷ 200) × 100 = 15%. This is useful for calculating test scores (points earned out of total), market share, or any proportional relationship.

Percentages are used everywhere: calculating discounts and sale prices, determining tax and tip amounts, analyzing investment returns, computing test scores and grades, measuring body fat percentage, tracking inflation rates, and evaluating survey results. Our calculator covers all these scenarios with dedicated modes for each calculation type.

To calculate a discount, use the percentage decrease method. If a $200 item has a 15% discount: 200 × (1 − 0.15) = $170 (sale price). The discount amount is $30. Alternatively, to find the discount percentage when you know both prices: use the % Change tab — ((170 − 200) ÷ 200) × 100 = −15%.

Percentage points refer to the absolute difference between two percentages. For example, if a rate rises from 10% to 15%, that's a 5 percentage point increase. However, the percent change is ((15 − 10) ÷ 10) × 100 = 50% (the rate increased by 50% relative to its original value). These are distinct concepts — our % Change tab calculates the latter.

Reverse percentage finds the original value before a percentage increase or decrease. If $170 is the price after a 15% decrease: Original = 170 ÷ (1 − 0.15) = 170 ÷ 0.85 = $200. For an increase: if $230 is after a 15% increase, Original = 230 ÷ (1 + 0.15) = 230 ÷ 1.15 = $200. While our calculator focuses on forward calculations, you can use the formulas to work backwards.

In Excel or Google Sheets, use these formulas: Percentage of a number — =A1*B1% or =A1*(B1/100); Percent one number is of another — =A1/B1 (format as %); Percentage change — =(B1-A1)/ABS(A1) (format as %); Increase by % — =A1*(1+B1%); Decrease by % — =A1*(1-B1%).