# How do you add 20% to a number?

Show Math (Enter values into the blue boxes. Select a different box to be the answer box if needed.)Answers are rounded to 7 decimal places.Percentage Calculator in Common Phrases:

Show Math

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Answers are rounded to 7 decimal places.

### Percentage Calculator in Common Phrases: seeexamples

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Answers are rounded to 7 decimal places.

#### Percent to Fraction to DecimalDecimal to Fraction to PercentPercentFractionDecimal%==

Answers are rounded to 7 decimal places.

## Add or Subtract a Percentage seeexamples

Calculate: tips, sales price, percent off, discounted price, price with sales tax, etc.

Start Value%ofStartValueEnd Value%=

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Answers are rounded to 7 decimal places.

#### Percent IncreasePercent Decrease

Use when comparing an old value to a new value or when comparing a start value to an end value.

Start ValueEnd ValuePercent Change%

A positive answer for percent change represents a percent increase.
A negative answer for percent change represents a percent decrease.
PercentChange=

End Value - Start Valueabs(Start Value)x100%
(where abs = absolute value)

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Answers are rounded to 7 decimal places.

Use when comparing a theoretical (known) value to an experimental (measured) value.

Theoretical ValueExperimental ValuePercent Error%

PercentError=

abs(Experimental Value - Theoretical Value)abs(Theoretical Value)x100%
(where abs = absolute value)

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Answers are rounded to 7 decimal places.

Use when comparing two values where neither value is considered a start value or a reference value.

One ValueAnother ValuePercent Difference%

Note: There is no standard equation for percent difference for all circumstances. The equation used here divides the difference between the two values by the average of the two values (see equation below). Some cases may require you to divide by the minimum of the two values or the maximum of the two values, etc. Please check that the equation used here fits your circumstance.
Equation used:
PercentDifference=

abs(One Value - Another Value)abs((One Value + Another Value)/2)x100%
(where abs = absolute value)

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Answers are rounded to 7 decimal places.

## Definitions:

### Percent:

Percent means per 100 or parts per 100. It can be used to describe a portion of a whole or part of a whole. It comes from per cent which is short for per centum which means per hundred.

The percent sign is: %

1 percent (1%) = 1 part per 100 = 1/100 = 0.01  (a portion less than a whole)
100 percent (100%) = 100 parts per 100 = 100/100 = 1  (a portion equal to a whole)
110 percent (110%) = 110 parts per 100 = 110/100 = 1.1  (a portion greater than a whole)

### Percentage:

An amount per 100 that refers to a portion of a whole (in a general way) typically without using a specific number.

### Percent vs. Percentage

The word percent is typically used with a number (example: 10 percent) while percentage is typically not used with a number (example: what percentage of the marbles are red?). An exception is percentage points (example: 2 percentage points).

### Percentage Calculator:

Calculator or tool that uses the percentage formula to solve for a desired value in that formula. The percentage formula contains three variables. If any two of the variables are known, the third variable can be calculated.

### Percentage Formula:

Formula used to solve percentage problems that relates two ratios where one of the ratios is a part or portion per 100 and the other ratio is a part or portion per a whole.

Where:
A% of B is C asin:10%of90is9  whereA=10,B=90,C=9

The percentage formula is:
A/100 x B = C asin:10/100x90=9

Rearranging:
A100 = CB  asin: 10100 = 990

The percentage formula is sometimes expressed as:
percent100 = is(part)of(whole) asin:10100=990

Solving for each of the variables yields:
A = (C / B) x 100 asin:A=(9/90)x100=10
B = C / (A / 100) asin:B=9/(10/100)=90
C = (A / 100) x B asin:C=(10/100)x90=9

Note: A% = A/100 because % means per 100

### How are percentages used?

• store discounts: 25 percent off sale
• sales tax is typically a percentage of purchase price: 8% sales tax
• interest rates for savings accounts are typically shown as an annual percentage rate (apr): 1.5% apr
• interest rates charged by credit card companies and mortgage companies are shown as an annual percentage rate.
• interest rate changes: interest rates rose one percentage point from 4.5% to 5.5%
• statistics: the margin of error is plus or minus four percentage points
• credit card rewards: 2% cash back for certain purchases
• news: approval ratings, employment rate, and surveys can be expressed using percentages
• laptops, tablets, and cell phones usually have a battery charge percentage indicator
• weather forecast: 20 percent chance of rain
• probability: the chance to win a prize is 1 in 10 or 10 percent
• humidity: the humidity level is 65%

Percentages can be used to make the relationship between a portion and a whole easier to understand.

Anytime you need to solve a percentage problem, the percentage calculator is here to help.