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Percentage Calculator

Calculate percentages, percent change, reverse percentages, percentage-point differences, and percentage add-ons or discounts.

Percentage inputs

Result

15% of 200 is 30
Formula
(15 / 100) x 200 = 30

How to use this percentage calculator

Use this calculator for quick percentage questions without setting up a spreadsheet or memorizing which formula goes with which wording.

  1. Choose the calculation type that matches your question.
  2. Enter the two numbers requested by the labels.
  3. Use the result panel to check the answer sentence and formula.
  4. Switch calculation types to reuse the same numbers in another percentage question.

Percentage Calculator features

  • Calculate what X percent of Y equals.
  • Calculate what percent one number is of another.
  • Calculate percentage increase or decrease.
  • Add a percentage to a number.
  • Subtract a percentage from a number.
  • Find the original value before a percentage change.
  • Show the answer sentence for each percentage mode.
  • Show the formula used for the selected calculation.
  • Switch calculation types while reusing the same numbers.

Common percentage calculations

This calculator handles everyday percentage questions: finding a percent of a number, finding what percent one value is of another, calculating percent increase or decrease, and adding or subtracting a percentage from a starting value.

Percentages show up in shopping discounts, tax, tips, invoices, growth reports, grade calculations, budgets, analytics dashboards, finance examples, and comparison tables. The confusing part is rarely the arithmetic itself; it is usually choosing the right interpretation of the question.

Use the calculation type as the first decision. If you are applying a rate to a number, choose "What is X% of Y?" If you are comparing a part to a whole, choose "X is what percent of Y?" If you are comparing before and after values, choose percentage increase or decrease. For sale prices, fees, markups, and reverse discounts, the adjustment and original-value modes keep the wording more explicit.

  • What is X% of Y? Use this percent of a number equation to calculate results like 15% of 200.
  • X is what percent of Y? Use this percentage of total equation to find the percent one number represents out of another.
  • Percentage increase or decrease. Use this percent change equation to compare an original value with a new value.
  • Add or subtract a percentage. Use this percentage adjustment equation for discounts, markups, tips, tax, and other increases or decreases.
  • Original value before percentage change. Use this reverse percentage equation to find the starting value before an increase, decrease, discount, or markup.

Percent means “per 100.” For example, 15% is the same as 15 out of 100, or 0.15 as a decimal.

Percentage formulas

The calculator changes the input labels and formula based on the selected question type. That keeps the same two input boxes useful for several common percentage problems while still showing the equation behind the result.

Percent of a number
R = \frac{P}{100} \times N

P is the percentage, N is the number, and R is the result.

Percent change
\Delta\% = \frac{New - Original}{Original} \times 100

A positive result is an increase. A negative result is a decrease.

Original value before percentage change
Original = \frac{Final}{1 \pm \frac{P}{100}}

Use plus for a final value after an increase and minus for a final value after a decrease or discount.

The displayed answer is rounded for readability, but the formula line is included so you can understand which values were used. For accounting, grading, or compliance work, apply the rounding rule required by that specific context.

Percentage calculator FAQ

How do I calculate a discount?
Choose add or subtract a percentage, enter the original price as the starting value, enter the discount percentage, and choose subtract percentage.
How do I calculate a percentage increase?
Choose percentage increase or decrease, enter the original value, then enter the new value. A positive result means the value increased.
What does reverse percentage mean?
Reverse percentage can mean finding the original value before a percentage increase or decrease. Choose Original value before percentage change for that calculation. If you need to find what percent one number is of another, choose X is what percent of Y.
Can percentages be over 100?
Yes. A percentage over 100 means the value is larger than the comparison value or more than the whole amount.
What is the easiest way to avoid choosing the wrong mode?
Read the question as a sentence. If it says 'of,' you are usually applying a percentage to a number. If it compares old and new values, use percent change. If it asks what the original price was before a discount or markup, use original value before percentage change.

Name the base before comparing percentages

Every percentage has a base. “Twenty percent” is incomplete until the reader knows twenty percent of what. Write the numerator, denominator, period, and population beside the result. A rate calculated from eligible users should not be compared with one calculated from all visitors without explaining the difference.

Percentage points and percent change are not the same. A rate rising from 20% to 25% increases by 5 percentage points and by 25 percent relative to the original 20%. Use percentage points for the direct difference between rates. Use percent change when the original value is the comparison base.

A decrease and an equal percentage increase do not cancel. Falling from 100 to 80 is a 20% decrease, but returning from 80 to 100 requires a 25% increase because the base changed. For successive discounts, growth rates, or markups, apply each step to the updated value rather than adding the percentages.

Small denominators can produce dramatic percentages. Moving from one event to two is a 100% increase but still only one additional event. Report the underlying counts and sample size, especially for safety, health, quality, and experiment metrics. Round at the end so intermediate rounding does not create a misleading total.

When reversing a percentage, state whether the known amount is before or after the change. A price after a 20% discount is 80% of the original, so dividing by 0.8 finds the original; adding 20% to the discounted price does not. Check the answer by applying the stated change forward.

Final check

  • Write the numerator, denominator, time period, population, and unit beside the result so the percentage has a clear base.
  • Report raw counts with rates, especially when a small denominator can turn one event into a dramatic relative change.
  • Distinguish percentage-point difference from percent change and use the original value as the relative-change base.
  • Apply sequential increases and decreases to the updated value rather than adding rates that use different bases.
  • Round only the displayed result, retain enough intermediate precision, and check a reverse calculation by applying the change forward.
  • Avoid causal or statistical claims from arithmetic alone; uncertainty, sampling, and study design need separate analysis.

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