Percentage, Discount & Percent Change Calculator

Percentages are among the most common numbers in daily life and among the easiest to get wrong: pay rises, share prices, test scores, revenue growth and shop discounts all depend on them. This tool groups the common cases into four modes. Enter your numbers and you get the result plus the full formula. “What is B% of A” calculates A × B ÷ 100, so 20% of 350 is 70. “A is what percent of B” calculates A ÷ B × 100, so 45 correct answers out of 60 is 75%.

Percent change works two ways. Compare mode takes an old and a new value and calculates (new − old) ÷ old × 100. Revenue rising from 80,000 to 100,000 is 25% growth, while falling from 100,000 back to 80,000 is a 20% drop, not 25%, because the base is different. Adjust mode increases or decreases a value by a percentage, so 1,000 plus 5% is 1,050. Successive changes cannot simply be added: a 10% rise followed by a 10% fall leaves you at 99% of the original, not back where you started.

Discount mode takes the unit price, discount rate and quantity, and shows the original total, the amount saved and what you pay. The discount rate is the percentage taken off, so “20% off” means entering 20 and paying 80% of the price. Promotions like “$10 off every $50” can be turned into an effective rate for comparison: $10 off $50 is 20% off. A “buy one, get one free” offer is effectively 50% off if you want both items.

Another common mix-up is percent versus percentage points. An interest rate moving from 2% to 3% rises by one percentage point, but in relative terms it rises 50%. News and financial reports usually use percentage points for changes in a rate itself. Every calculation runs instantly in your browser, with results shown to up to six decimal places.