Percentage Calculator

Percentage calculations come up constantly: discounts, test scores, tax, tips, statistics. This calculator handles all three standard percentage question types at once: finding a percent of a number, finding what percent one number is of another, and finding the base when you know the percentage.

• Discounts and sales: 30% off $85: what is the sale price? Mode 1 gives you 30% of 85 = $25.50 off, so the sale price is $59.50.
• Test scores: Got 42 out of 55: what percentage? Mode 2 gives 42/55 × 100 = 76.36%.
• Tax and tips: Bill is $47: what is 18%? Mode 1 gives 18% of 47 = $8.46.
• Finding the whole: 30 is 40% of what number? (Mode 3 → 75)

1. 1Enter Value A and Value B.
2. 2Choose a mode: 1 to find A% of B, 2 to find what percent A is of B, or 3 to find the number that A is B% of.
3. 3The calculator shows the answer for all three modes simultaneously.

• Confusing "percent of" with "percent change": "10% of 200" is 20. "10% more than 200" is 220. These are different operations. The mode selector in this calculator keeps them separate, but it is easy to pick the wrong one.
• Applying percentage change in the wrong direction: A 20% increase followed by a 20% decrease does not return to the original value. 100 + 20% = 120, then 120 - 20% = 96. Percentage changes compound asymmetrically.
• Confusing basis points with percentage points: A rate moving from 3% to 4% is a 1 percentage-point increase, but it is a 33% relative increase. These mean very different things. Financial writing often uses "basis points" (100 bps = 1 percentage point) to avoid ambiguity.
• Rounding the base before calculating: If your base is 237 but you round it to 240 for convenience, the percentage will be slightly off. Use the exact figure in the calculator, then round the result.

• Use mode 3 (find the whole) for reverse calculations: If you know the discounted price and the discount percentage, use mode 3 to find the original price. This is common in retail: $85 after 15% off. Original = 85 ÷ 0.85 = $100.
• Check percentage change symmetry: If a stock rises 50% and falls 50%, you end up with 75% of the starting value, not 100%. Verify this with the percentage change mode by running both calculations sequentially.
• Convert decimals to percentages for readability: Multiply by 100 to convert a decimal to a percentage. 0.0375 = 3.75%. When reading financial statements, check whether a rate is expressed as a decimal or percentage before using it in a formula.
• Use it to sanity-check a salesperson's math: If a discount is quoted as "save $47 off a $235 item," enter 47 and 235 to verify the stated percentage. A 20% discount should save $47. Anything else is either a rounding error or a pricing trick.