Percentage Calculator

Percentages express a part relative to a whole out of 100. This calculator covers four everyday patterns: finding X% of Y, finding what percent X is of Y, increasing Y by X%, and decreasing Y by X%. Pick the mode that matches your question — the labels Value X and Value Y change meaning slightly by mode, but the math stays consistent.

Percent of a number: result = Y × (X ÷ 100). With the default fields (15% of 200), that is 200 × 0.15 = 30. Use this when a sale tag says "15% off eligible items" and you want the dollar amount, or when a recipe calls for 15% of a weight.

What percent is X of Y: result = (X ÷ Y) × 100. If you scored 45 points out of 200 possible, (45 ÷ 200) × 100 = 22.5%. This mode answers "what fraction of the whole is this?" — useful for test scores, budget burn rates, and comparing spending categories.

Increase Y by X%: new value = Y × (1 + X/100). A 15% raise on a $200 weekly grocery budget grows it to 200 × 1.15 = $230. Decrease Y by X%: new value = Y × (1 − X/100). The same 15% cut on $200 leaves 200 × 0.85 = $170. Increase and decrease apply to the base Y, not to some other reference number.

A common mistake is adding percentages incorrectly when stacking discounts. A 20% off coupon followed by 10% off is not 30% off the original — the second discount applies to the already-reduced price. Use decrease mode twice in sequence rather than adding the percents. Another mistake is confusing "percent of" with "percent increase": 15% of 200 is 30, but 200 increased by 15% is 230, not 215.

Percentage points differ from percent change. If a rate rises from 10% to 15%, that is a 5 percentage-point increase, but the relative change is (15 − 10) ÷ 10 = 50% growth. This tool does not compute percentage-point differences — enter the two values in "what percent" mode if you need a ratio.

Reverse calculations: if you know the final amount after a 15% increase should be $230, divide by 1.15 to find the original $200 — this tool forward-calculates only; work backward with division when solving for the starting value.

Spreadsheet users write =200*0.15 for percent of, =45/200 for what percent, and =200*1.15 for increase — the mode picker here replaces memorizing which formula fits which question.

Fitness and nutrition labels use percent daily value based on a 2,000-calorie reference diet — that percent is not "what percent of your meal is protein" unless you define the whole correctly in what-percent mode.

Grade school math phrasing "find 15 percent of 200" maps directly to percent-of mode with X=15 and Y=200 — keep X as the rate and Y as the whole to avoid swapped results.

Tip math is percent-of: a 20% tip on an $85 check is percent-of with X=20 and Y=85 — the dedicated tip calculator also splits among people if you need that extra step.

Engineering tolerance specs sometimes allow ±5% variation — decrease mode on the nominal value shows the lower bound of an acceptable range.

Limits: results assume X and Y are positive unless your use case allows negatives (debt paydown, temperature). Division by zero when Y is 0 is undefined — enter a non-zero denominator. The calculator does not format results as fractions or show step-by-step algebra; it returns the numeric answer for the selected mode.