# Percentage Calculator > Fifteen percentage calculators that ask their question as a sentence, answer > as you type, and show the arithmetic underneath the answer. No accounts, no > sign-up, and no button the reader has to press. ## What this site is Most percentage calculators put three unlabelled boxes under a heading and leave the reader to work out which box is which. This one writes the question out instead: **"What is [ 15 ]% of [ 200 ]?"**, with the input boxes set into the sentence where the numbers belong. A reader who cannot remember whether they want percent change or percent difference can read the sentence and know. That is the whole design idea, and the rest of the site follows from it. Everything else is in service of the same goal — a calm page that gives a plain answer: - **The answer appears as you type.** There is no "Calculate" button to press, and no page reload. - **The working is shown under every answer**, with the reader's own numbers substituted into the formula. The site is meant to teach the sum, not only to do it. - **A quiet palette.** Soft ice-blue and off-white grounds, one accent colour, and a single type scale. The page follows the reader's system light or dark setting; there is no theme switch to find. - **An empty box means "no answer", never zero.** An empty field returns a blank result rather than a confident wrong one. - **Float noise is removed.** Results are rounded to 12 significant digits, which is inside double precision, so `0.07 × 3` reads `0.21` and not `0.21000000000000002`. ## Linking to a filled-in calculator Every calculator reads its starting numbers from the query string, so an assistant can send a reader to a page that already holds their numbers and already shows their answer. The parameters are listed with each formula below. https://percentagecalcs.com/?p=15&x=200 https://percentagecalcs.com/percent-off-calculator?price=80&off=25 https://percentagecalcs.com/win-percentage-calculator?w=11&l=5&t=1 An unknown or non-numeric parameter is ignored rather than rejected, and the canonical URL of every page is the bare path with no query string. ## Calculators - [Percentage Calculator](https://percentagecalcs.com/): Work out what is X% of Y, what percent one number is of another, and the number a percentage came from. Three calculators, instant answers, every step shown. - [Percentage Increase Calculator](https://percentagecalcs.com/percentage-increase-calculator): Increase any number by a percentage, or find the percentage increase between two numbers. Shows the formula with your numbers substituted in. - [Percent Change Calculator](https://percentagecalcs.com/percent-change-calculator): Find the percent change from one value to another. Handles increases, decreases and negative starting values correctly, and shows the working. - [Percentage Decrease Calculator](https://percentagecalcs.com/percentage-decrease-calculator): Decrease a number by a percentage, or find the percentage decrease between two numbers. Instant answer with the formula shown. - [Percent Difference Calculator](https://percentagecalcs.com/percent-difference-calculator): Percent difference compares two values where neither is the original. It divides by their mean, so the answer is the same whichever order you enter them. - [Percent Error Calculator](https://percentagecalcs.com/percent-error-calculator): Compare a measured value with the accepted value and get the percent error. Shows both the unsigned school formula and the signed version. - [Percent Yield Calculator](https://percentagecalcs.com/percent-yield-calculator): Divide the actual yield of a reaction by the theoretical yield to get the percent yield. Works in grams or moles, and shows the formula. - [Percent Off Calculator](https://percentagecalcs.com/percent-off-calculator): Take a percentage off any price and see both the saving and the final price. Also works backwards from a sale price to the discount. - [Percentile Calculator](https://percentagecalcs.com/percentile-calculator): Find the value at any percentile of a data set, or the percentile rank of one value inside it. Matches Excel's PERCENTILE.INC. - [Average Percentage Calculator](https://percentagecalcs.com/average-percentage-calculator): Averaging percentages by adding them up only works when every group is the same size. This weights each percentage by its group size. - [Grade Percentage Calculator](https://percentagecalcs.com/grade-percentage-calculator): Turn a score out of a total into a percentage and a letter grade. Enter points earned and points possible for an instant result. - [Win Percentage Calculator](https://percentagecalcs.com/win-percentage-calculator): Work out a winning percentage from a record. Ties count as half a win, the convention the NFL and US college sport both use. Shows the formula. - [Weight Loss Percentage Calculator](https://percentagecalcs.com/weight-loss-percentage-calculator): See what percentage of your starting weight you have lost. Enter a start weight and a current weight in any unit, and the calculator shows the formula. - [Fraction to Percent Calculator](https://percentagecalcs.com/fraction-to-percent-calculator): Convert a fraction to a percentage and back. Enter a numerator and a denominator, or a percentage to get the fraction in lowest terms. - [Decimal to Percent Calculator](https://percentagecalcs.com/decimal-to-percent-calculator): Turn a decimal into a percentage or a percentage into a decimal. Converts both ways at once, with no rounding errors, and shows the working. ## Formulas and parameters Each block gives the arithmetic the page runs, the query parameters it reads, and any convention where sources reasonably differ. ### Percentage Calculator https://percentagecalcs.com/ part = percent ÷ 100 × whole percent = part ÷ whole × 100 whole = part ÷ percent × 100 change = (to − from) ÷ |from| × 100 Parameters: - `p, x — what is p% of x` - `a, b — a is what percent of b` - `c, d — c is d% of what number` - `f, t — percent change from f to t` All four questions are on the one page, each written as a sentence with the numbers set into it. ### Percentage Increase Calculator https://percentagecalcs.com/percentage-increase-calculator increase = (to − from) ÷ |from| × 100 result = value × (1 + percent ÷ 100) Parameters: - `from, to — increase between two values` - `v, p — add p% to v` ### Percent Change Calculator https://percentagecalcs.com/percent-change-calculator change = (to − from) ÷ |from| × 100 Parameters: - `from, to — the two values` The denominator is the absolute value of the starting number, so a change from −50 to 25 is +150%, not −150%. ### Percentage Decrease Calculator https://percentagecalcs.com/percentage-decrease-calculator decrease = (from − to) ÷ |from| × 100 result = value × (1 − percent ÷ 100) Parameters: - `from, to — decrease between two values` - `v, p — take p% off v` ### Percent Difference Calculator https://percentagecalcs.com/percent-difference-calculator difference = |a − b| ÷ ((a + b) ÷ 2) × 100 Parameters: - `a, b — the two values` Percent difference divides by the mean of the two values, so the answer is the same in either order. It is not percent change, which divides by the first value. ### Percent Error Calculator https://percentagecalcs.com/percent-error-calculator error = |observed − actual| ÷ |actual| × 100 signed error = (observed − actual) ÷ |actual| × 100 Parameters: - `obs, act — observed value and accepted value` The page shows both. The unsigned form is the school formula; the signed form keeps the direction of the error. ### Percent Yield Calculator https://percentagecalcs.com/percent-yield-calculator yield = actual ÷ theoretical × 100 Parameters: - `actual, theo — actual yield and theoretical yield` Units cancel, so grams or moles both work as long as both boxes use the same one. ### Percent Off Calculator https://percentagecalcs.com/percent-off-calculator saving = price × percent ÷ 100 final = price − saving discount = (original − sale) ÷ original × 100 Parameters: - `price, off — take off% off price` - `orig, sale — the discount between two prices` ### Percentile Calculator https://percentagecalcs.com/percentile-calculator rank = p ÷ 100 × (n − 1), then interpolate between the two neighbouring sorted values percentile rank = (count below + 0.5 × count equal) ÷ n × 100 Parameters: - `data — the data set, comma or space separated, e.g. data=2,4,4,5,9` - `p — the percentile to look up` - `v — the value to rank` The value lookup matches Excel PERCENTILE.INC and NumPy's linear method. Other definitions exist and give different answers near the ends of a small data set. Unreadable entries in `data` are dropped rather than failing the whole list. ### Average Percentage Calculator https://percentagecalcs.com/average-percentage-calculator average = Σ(percentᵢ ÷ 100 × sizeᵢ) ÷ Σ sizeᵢ × 100 No URL parameters — the rows are entered on the page. Percentages are weighted by group size. Adding percentages and dividing by their count is only correct when every group is the same size. ### Grade Percentage Calculator https://percentagecalcs.com/grade-percentage-calculator percent = earned ÷ possible × 100 Parameters: - `earned, total — points earned and points possible` The letter grade uses the common US scale: A 90+, B 80+, C 70+, D 60+, F below 60. ### Win Percentage Calculator https://percentagecalcs.com/win-percentage-calculator win% = (wins + ties ÷ 2) ÷ (wins + losses + ties) × 100 Parameters: - `w, l, t — wins, losses, ties` A tie counts as half a win, the convention in the NFL and in US college sport. A team that ties every game sits at exactly 50%. The NHL is the exception: it has had no ties since 2005-06, and its standings use a points percentage that this formula does not reproduce. ### Weight Loss Percentage Calculator https://percentagecalcs.com/weight-loss-percentage-calculator lost% = (start − current) ÷ start × 100 Parameters: - `start, now — starting weight and current weight` Any unit works, as long as both boxes use the same one. ### Fraction to Percent Calculator https://percentagecalcs.com/fraction-to-percent-calculator percent = numerator ÷ denominator × 100 fraction = percent ÷ 100, reduced by the greatest common divisor Parameters: - `n, d — the fraction` - `p — a percent to convert back` ### Decimal to Percent Calculator https://percentagecalcs.com/decimal-to-percent-calculator percent = decimal × 100 decimal = percent ÷ 100 Parameters: - `d — a decimal to convert` - `p — a percent to convert` ## Conventions used across the site - **Percent change divides by the first value; percent difference divides by the mean of both.** They answer different questions and rarely agree. - **A negative starting value keeps its sign out of the denominator.** Percent change uses `|from|`, so a rise from −50 to 25 reads as +150%. - **Percentages do not compose.** 10% off then 10% on returns 99, not 100, because each percentage applies to a different base. - **Nothing is rounded before the final step.** Rounding happens once, for display. ## Optional - [Feedback](https://percentagecalcs.com/feedback): Report a wrong answer or ask for a calculator. - [Privacy](https://percentagecalcs.com/privacy): What the site stores. No accounts, no personal data. - [Terms](https://percentagecalcs.com/terms): Terms of use. - [Sitemap](https://percentagecalcs.com/sitemap.xml): every indexable URL on the site.