A calculator is always helpful when determining percentages, but you can easily compute percentages without a calculator. A pencil and paper might be helpful as you do this.
Make the percentage a fraction
Determine what the percentage you are trying to find would be. For example, if you wanted to calculate 33 percent of a number, you would use the fraction 1/3.
Divide the number you are trying to find the percentage of by the denominator
Take the number you want to find the percentage of (for this example, assume it is 21) and divide it by the denominator, which is the bottom number of the fraction.
Determine the answer
Divide 21 by 3 and you find that the answer is 7. This model works any time you want to find the percentage of a number.
Check your answer
Take the answer that you calculated and multiply it by the denominator. The answer you receive should be the number for which you were originally trying to find the percentage. In this example, multiplying the denominator of 3 by the answer you calculated, which was 7 verifies that the answer is correct because the result is the original number of 21.