Percentage Calculator

A multi-mode percentage calculator that handles the three most common percentage questions: "What is X% of Y?" (e.g., 15% of 200 = 30), "X is what percent of Y?" (e.g., 45 is 25% of 180), and "What is the percentage change from X to Y?" (e.g., 80 to 100 = 25% increase).

Results update instantly as you type. Quick example buttons let you load common scenarios in one click. All calculations run in your browser — nothing is sent to any server.

**Understanding Percentage Calculations**

Percentages are a fundamental part of everyday mathematics and are used extensively in finance, business, shopping, cooking, and statistics. A percentage represents a number as a fraction of 100. The word comes from the Latin "per centum," meaning "by the hundred." Understanding how to calculate percentages quickly and accurately is one of the most practical mathematical skills.

**The Three Modes Explained**

Mode 1 — "What is X% of Y?" This calculates a specific portion of a number. The formula is: Result = (X ÷ 100) × Y. For example, 15% of R2,500 = (15 ÷ 100) × R2,500 = R375. This is useful for calculating tips, discounts, tax amounts, or commission. A salesperson earning 12% commission on a R50,000 sale would earn R6,000.

Mode 2 — "X is what percent of Y?" This finds what percentage one number is of another. The formula is: Percentage = (X ÷ Y) × 100. For example, R450 is (R450 ÷ R3,000) × 100 = 15% of R3,000. This is useful for analysing budgets, measuring progress toward goals, or understanding proportions. If your rent is R8,000 and your salary is R40,000, rent is 20% of your income.

Mode 3 — "Percentage change from X to Y." This measures the relative change between two values. The formula is: Change = ((Y − X) ÷ |X|) × 100. A positive result means an increase, negative means a decrease. For example, if a product price rises from R150 to R180, the percentage increase is ((180 − 150) ÷ 150) × 100 = 20%. If it drops from R180 to R150, the percentage decrease is ((150 − 180) ÷ 180) × 100 = −16.67%.

**Real-World Applications**

In South African personal finance: If your salary increases from R35,000 to R38,500 per month, that is a 10% increase. If inflation is 5.5%, your real increase (above inflation) is approximately 4.5%. If a R1,200 item goes on sale for R960, the discount is 20%. If your investment portfolio grows from R100,000 to R112,000, your return is 12%.

In business: If your monthly revenue is R250,000 and cost of goods sold is R150,000, your cost percentage is 60% of revenue. If your website conversion rate is 3%, that means 3 out of every 100 visitors make a purchase. If you want to increase revenue by 15%, you need to go from R250,000 to R287,500.

**Tips for Working with Percentages**

Remember that percentage increases and decreases are not symmetric — a 20% increase followed by a 20% decrease does not return you to the original value. A R100 item increased by 20% becomes R120; a 20% decrease on R120 brings it to R96, not R100. Be careful with percentage points vs. percentages: if an interest rate rises from 8% to 10%, that is a 2 percentage point increase, but a 25% relative increase. When comparing percentage changes, always note the base value — a 50% increase on R100 is R50, but a 50% increase on R1,000 is R500.