How To Calculate Percentages Quickly In Your Head

Easy Way to Calculate a 15% Tip

Rule of thumb — standard service — 15%. The most commonly used shortcut to 15% is to find 10% and then add a half. This is an easy calculation, since all you need to do to find 10% is move the decimal point one space to the left (make the number smaller).

Consider a bill for 47.31. First impressions show us 10% is 4.70 and a half of this amount is 2.35, so a tip of 7.00 is reasonable. This is a simplification as we can do the exact math — 4.70 add 2.35 is 7.05 — but we are looking for an easy method, not an exacting science. Another sound strategy is to work from the highest place value, in other words, if the bill is in the 50s then the tip should be in the 7.50 range. If the bill is 124.00, the logic follows that 12 add 6 =18 so a total of 124 add 18 or 142 is reasonable.


About Percentage Calculator:

An online percentage calculator by calculator-online helps you to calculate percentage and unknown percent values in equations. The tool uses simple formula for percentage to calculate percentages of the given equation. Also, this percent calculator allows you to add or subtract a percentage form a number or solve the equations.

How to Figure Out Percentages With This Percentage Calculator:

The calculator is 100% free and allows you to perform percentage calculation or what percent of (any number) within a fraction of seconds. You can easily and accurately determine % age, or more with the assistance of this calculator. Just stick to these steps to obtain the precise measurements corresponding to the percentages.


  • First of all, you have to choose the equation for which you want to calculate the percentage
  • Then, you have to enter the values into the designated fields corresponding to the selected equation
  • Once done, just hit the calculate button to actual percentage value


The percent calculator shows:

  • Percentage value according to the selected percentage equation
  • Show the step-by-step calculation for the equation

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How to Do Percentages In Your Head

So how much is 15 percent of 210? You can use the four key percentages you memorized to figure this out. Consider that 15 percent is 5 percent added to 10 percent. Since 10 percent of 210 is 21, and 5 percent is half that, or 10.5, then 15 percent is 21 added to 10.5, or 31.5.

How about 75 percent of 440? Here you can figure that 75 percent is 50 percent added to 25 percent. Since 50 percent of 440 is half that, or 220, and 25 percent of 440 is one fourth, or 110, then 75 percent is 220 added to 110, or 330.

In this way you can combine 5 percent, 10 percent, 25 percent, and 50 percent to calculate a wide variety of percentages in your head. If you need to calculate a percentage that is not a multiple of 5, you can use this technique to estimate the answer very closely.


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How to get the percentage in Excel

If you were working on an Excel spreadsheet with data, we can set the automatic calculation to get a percentage on different figures. For example, if you had to apply a saving of 15% on four different expenses, and you want to know how much that percentage represents, the following steps should be followed:

  1. Establish in a column, in this case, B, for the different expenses.
  2. Choose a second column, C, to indicate the percentage of savings we want to achieve, in this case, 15%.
  3. In the third column, we are going to write the formula, which is: = B2 * (1-C2)

In this formula, 1 is equivalent to 100%. The values ​​in parentheses are calculated first, so the value of C2 is subtracted from 1, to give us 85%. The result is multiplied by B2 to obtain a result of 7253.9 for expense 1. That would be the expense that must be reached with the 15% savings sought.

To copy the formula from cell D2 down, double-click the box in the lower right corner of cell D2. Results are obtained in all other cells without having to copy and paste the formula again.

How to get a percentage with a calculator

For example, if you want to get 20% of 5684, you must write that amount first: 5684.

Then it is multiplied by 20, which in this case is the percentage that needs to be calculated. And then the% key is pressed. This function delivers the result directly. In this case, 1136.8 is 20% of 5684.

You can also use the percentage (%) function of the combined calculator in addition or subtraction to directly calculate increases or discounts.

First, the number is written (in this case 4456), then it is added by the percentage (15) and the% key is pressed. Their many calculators indicate the partial figure of a 15% increase; and when pressing the equal (=) they give the result with the included increment (5124.4). Others give the final result directly. The same goes for a subtraction.

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Percentage of exercises

One of the most frequent exercises is when we must add the Value Added Tax (VAT) to a product or service because initially the amount is disaggregated. The final consumer VAT is 21%.

So, if you have to pay a service of $3966 + VAT, you have to calculate how much is 21% of 3966.

According to the different manual calculations, the most practical way to calculate the percentage would be:

3966/100 x 21 = 832.86

If done with a calculator, you can directly write the result of the division by running the decimal two places to the left: 39.66, then you do a single step: 39.66 x 21.

Working with Percentages

We calculated a 20% discount in the example above and then subtracted this from the whole to work out how much a new laptop would cost.

As well as taking a percentage away, we can also add a percentage to a number. It works exactly the same way, but in the final step, you simply add instead of subtracting.

For example: George is promoted and gets a 5% pay rise. George currently earns £24,000 a year, so how much will he earn after his pay rise?
  1. Work out 1% of the whole

    The whole in this example is George’s current salary, £24,000. 1% of £24,000 is 24,000 ÷ 100 = £240.

  2. Multiply that by the percentage you are looking for

    George is getting a 5% pay rise, so we need to know the value of 5%, or 5 times 1%.

    £240 × 5 = £1,200.

  3. Complete the calculation by adding to the original amount

    George’s pay rise is £1,200 per year. His new salary will therefore be £24,000 + £1,200 = £25,200.

    Percentages over 100% It is possible to have percentages over 100%. This example is one: George’s new salary is actually 105% of his old one. However, his old salary is not 100% of his new one. Instead, it is just over 95%. When you are calculating percentages, the key is to check that you are working with the correct whole. In this case, the ‘whole’ is George’s old salary.

Percentages as Decimals and Fractions

One percent is one hundredth of a whole. It can therefore be written as both a decimal and a fraction.

To write a percentage as a decimal, simply divide it by 100.

For example, 50% becomes 0.5, 20% becomes 0.2, 1% becomes 0.01 and so on.

We can calculate percentages using this knowledge. 50% is the same as a half, so 50% of 10 is 5, because five is half of 10 (10 ÷ 2). The decimal of 50% is 0.5. So another way of finding 50% of 10 is to say 10 × 0.5, or 10 halves.

20% of 50 is the same as saying 50 × 0.2, which equals 10.

17.5% of 380 = 380 × 0.175, which equals 66.5.

George’s salary increase above was 5% of £24,000. £24,000 × 0.05 = £1,200.

The conversion from decimal to percentage is simply the reverse calculation: multiply your decimal by 100.

0.5 = 50% 0.875 = 87.5%

To write a percentage as a fraction, put the percentage value over a denominator of 100, and divide it down into its lowest possible form.

50% = 50/100 = 5/10 = ½ 20% = 20/100 = 2/10 = 1/5 30% = 30/100 = 3/10


It is possible to convert fractions to percentages by converting the denominator (the bottom number of the fraction) into 100.

However, it is harder to convert fractions to percentages than percentages to fractions because not every fraction has an exact (non-recurring) decimal or percentage.

If the denominator of your fraction does not divide a whole number of times into 100, then there will not be a simple conversion. For example, 1/3, 1/6 and 1/9 do not make ‘neat’ percentages (they are 33.33333%, 16.66666% and 11.11111%).


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