Percentage Calculator
Calculate percentages in three ways: X% of Y, X is what % of Y, and X increased or decreased by Y%. Instant result.
How to calculate percentage?
X% of Y: just multiply Y by X and divide by 100. See: 10% of 200 = 20.
X is what % of Y: divide X by Y and multiply by 100. For example, 20 is 10% of 200.
Increase/decrease: multiply Y by (1 ± X/100). So 200 + 10% = 220 and 200 − 10% = 180.
How percentage math works
A percentage expresses a ratio out of one hundred — the word comes from Latin per centum. Three operations cover almost every real-world case. First, X% of Y: result = X · Y / 100. Example: 15% of 80 equals 15 · 80 / 100 = 12. Second, part over whole: % = part / whole · 100. If 23 of 50 students passed, the pass rate is 23 / 50 · 100 = 46%. Third, percentage change: Δ% = (new - old) / old · 100. A price moving from R$ 200 to R$ 230 represents a (230 - 200) / 200 · 100 = 15% increase.
A classic pitfall: a 10% increase followed by a 10% discount does not return to the original value. Start with 100, add 10% to get 110, then take 10% off to get 99 — a net loss of 1%. The same logic explains why a stock that drops 50% needs to rise 100% to recover, not 50%. Successive percentages multiply (1.10 · 0.90 = 0.99), they do not simply add.
Common applications
- Retail discounts, sales tax and tip calculations.
- Inflation indices such as IPCA, IGP-M and CPI applied to rent, contracts and salaries.
- Investment returns, CDB and savings account yield comparison.
- Simple and compound interest baseline (the rate itself is a percentage per period).
- Standardized exams such as ENEM, vestibular and concursos públicos, where percentage problems are heavily weighted.
FAQ
How do I take a percentage off a price? Multiply by (1 - X/100). For 20% off R$ 250: 250 · 0.80 = R$ 200.
Does a 50% drop need a 50% gain to recover? No. After a 50% drop, you need a 100% gain to return to the original value, since the new base is half the original.
What is the difference between percentage and percentage points? Going from 4% to 6% is a 2 percentage-point rise but a 50% increase in relative terms. News headlines often confuse the two.
Can a percentage exceed 100%? Yes, whenever the part is greater than the whole. A company that doubles revenue grew 100%; one that triples grew 200%.
Solve any percentage problem
Store discount, rent increase, test score, credit-card interest: percentages turn up everywhere. The annoying part is that each case calls for a slightly different calculation, and that's exactly where people get stuck. This calculator handles the most common ones so you don't have to recall the formula from memory.
You can find what a percentage of a value is (15% of 200), what percentage one number is of another (45 is what % of 180), plus the percentage increase or decrease between two values. Enough to check a sale, split a tip, make sense of a price change, or adjust a recipe.
As you fill in the fields the result already shows up, no need to press equals. The whole calculation runs in the browser, so it keeps working offline once the page has loaded.
Frequently asked questions
How do I work out the percentage change between two values, say 200 to 230?
Which field is which in each mode?
Why does the result show a dash or an infinity sign?
Related Tools
Niacinamide Cream Percent
Estimates niacinamide concentration by skin goal.
Xanthan Thickener Percentage Amount Calculator
Computes the amount of xanthan gum in grams for a target thickening from the liquid volume and the recommended percentage.
Glucose Crystallization Percentage Amount Calculator
Computes the amount of glucose in grams to avoid crystallization of syrup from sucrose weight and the target percentage.
Pulp Dilution Water
Computes how much water must be added to take a pulp from one mass percent solids to a lower one, Water = M × (C₁/C₂ − 1), where M is the incoming pulp mass (or mass flow). It follows from the mass balance: the solids mass does not change on dilution, so the final pulp mass is M·C₁/C₂ and the difference is water. This is the most routine operation in a mineral processing plant — grinding, desliming, flotation and thickening each demand their own percent-solids range, and getting the dilution water wrong throws off residence time, viscosity and reagent consumption. Both percentages are by mass (weight of solids per weight of pulp), and the result comes out in the same unit entered for M. Enter the pulp mass or flow, the current percent solids and the target percent solids.
Discount Calculator
Calculate the discount amount and final price from the original price and discount percentage. Instant result.
VIX Implied Volatility
Estimate the market annualized implied volatility from the VIX level, the so-called fear index. Understand what the VIX number projects for the S&P 500.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.