Spike's Calculators

# Calculate With Percentages

Percentages are used everywhere. For example, you have to make a down payment based on a percentage of the starting amount; your construction mortgage draws are split up and paid in draws based on percentages. If you are building a home, guaranteed you would run into something expressed in a percent value. The slope of a garage slab, a deck slope, the laying of septic field pipes, etc., you will have to make the basic calculations using percentages!

Or, if all fails, you can use one of these calculators.

## Calculating a percentage of an amount

The easiest way of calculating a percentage of an amount for me is to divide the amount by 100 to get the 1% value and then multiply that with the percentage amount.
```starting amount = 240 ( 100%)
percentage = 12%```

divide 240 to 100 to get the 1% value
`240 ÷ 100 = 2.40`
`one percent of 240 = 2.4`

calculate what 12% is by multiplying the one percent amount of 2.4 by 12;
`2.4 * 12 = 28.8`
`12% of 240 equals 28.8`

### As a fraction of an amount

Make it even more confusing. At times you have to subtract an amount expressed as a fraction.
```starting amount = 240
fraction = 3/25```

covert the fraction to a decimal by dividing the numerator 3 by the denominator of 4;
`12 ÷ 100 = 0.12 (if you multiply 0.12 by 100 you get the percent value; 0.12 * 100 = 12%)`
multiply the starting amount of 240 by decimal 0.12
`240 * 0.12 = 28.8`
`3/25 of 240 equals 28.8`

### Percentage of an amount by converting the percentage to a decimal

A much simpler way of doing a calculation using percent values.
```Starting amount = 240 = 100%
Percentage = 12%```

Convert the 12% to a decimal number by dividing it by 100
`12 ÷ 100 = 0.12`
`12% in a decimal is 0.12`

multiply the starting amount of 240 by decimal 0.12;
`240 * 0,12= 28.8`
`and again 12% of 240 = 28.8`

## Calculating a Discount Percentage

With a discount in a percentage, the percentage discount reduces the starting amount. If the starting amount is equal to 100%, and the discount is 24%, then the final amount you pay is 100% - 24% = 76% of the starting amount.
##### Example calculation;
```starting amount = \$369.55
discount = 11%```

If \$369.55, the starting amount is equal to 100% after applying the 11% discount, the new price will be 100% - 11% = 89% of the starting amount.

Convert 89% to a decimal number by dividing 89 by 100;
`89 ÷ 100 = 0.89`
`89% in a decimal is 0.89`

multiply the starting amount of \$369.55 by the decimal0.89;
`369.55 * 0.89 = 328.8995 rounded to 328.90`
`The starting amount of \$369.55 after applying an 11% discount is \$328.90`

11% of \$369.55
If all you need to know what 11% is in a dollar value, first convert the 11% to a decimal by dividing it by 100;
`11 ÷ 100 = 0.11`
`11% in a decimal is 0.11`

multiply \$369.55 by decimal 0.11 ;
`369.55 * 0.11 = 40.6505 rounded to 40.65`
`11% of \$369.55 is \$40.65`

##### Alternate Way
An alternate way which some of us find easier to do;
divide the \$369.55 by 100 and multiply the result by 11;
`369.55 ÷ 100 = 3.6955 * 11 = 40.6505 rounded to 40.65`
`The discount equals \$40.65.`

### Calculating a Surcharge Percentage

A surcharge percent is a percentage added to a starting amount, which means that the amount increases. If the starting amount equals 100% and the surcharge is 30%, then the final amount will equal 130% of the starting amount. Done much the same way as with a discount, but instead of reducing, it increases the starting amount.

##### Example calculation;
```starting amount = \$1200.00
surcharge = 30%```

if \$1200.00 is the starting amount, and equal to 100% after applying the 30% surcharge, the new price will be 130% of \$1200.00.

convert the 130% to a decimal number by dividing 130 by 100;
`130 ÷ 100 = 1.3`
`130% in decimal is 1.3`

multiply the starting amount of \$1200.00 by the decimal 1.3 to get the final amount;
`1200.00 * 1.3 = 1560`
`The starting amount of \$1200.00, with a 30% surcharge, is \$1560.00`

30% of \$1200.00
If all you need to know what 30% is in a dollar value, first convert the 30% to a decimal by dividing it by 100;
`30 ÷ 100 = 0.3`
`30% in a decimal is 0.3`

multiply \$1200.00 by decimal 0.3
`1200 * 0.3 = 360`
`30% of \$1200 is \$360`

##### Alternate Way
Again an alternate way which some of us find easier to do;
divide the \$1200 by 100 and multiply the result by 30;
```1200 ÷ 100 = 12 * 30 = 360
The surcharge amount is \$360.00

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