How Do I Work Out Percentage Without A Calculator?

You can easily change decimal numbers to percentages and vice versa by multiplying or dividing by 100%, respectively. This is equivalent to moving the decimal point two places and adding/removing the percent sign.
  Examples: 1.20 = 120%, .03% = .0003, 10% = .10, 1/5 = 1/5*100% = 20%

Given the above, your question is equivalent to "how do I do math without a calculator?" You do it the "old-fashioned" way, with pencil and paper, or you learn how to do it in your head.

There are several useful facts that can help you do math in your head.

• Approximation and estimation skills are useful. Most mental calculations need be done to no better than 3 significant digits, and often 2 are sufficient.
  
• Finding 10% of a number involves only moving the decimal point one place to the left.
  
• Finding 5% of a number involves moving the decimal point one place left and division by 2, in either order.
• 15% = 10% + 5%    (add half of 10% to 10%)
  
• 20% = 1/5 = 10% + 10%    (Move the decimal point, then add the result to itself.)
  
• 25% = 1/4 = (1/2)*(1/2)    (Divide by 2, then divide that result by 2.)
• 90% = 1 - 10%    (subtract 10% from the number to get 90% of it)
• For numbers x slightly smaller than 1 (100%), 1/x ≈ 1+ (1-x)  (Example: 1/.9 ≈ 1.1)
• For numbers x slightly larger than 1, 1/x ≈ 1- (x-1)  (Example: 1/1.1 ≈ .9)  These last two approximations have more error as you get further away from 1.
  

What percentage you want to find out, just multiply that with the actual amount and then divide the answer by 100. You will get the percentage of that amount. Or other easy steps, suppose you want to find out 20 % of 500, then remove last zero from 500, what you remain is 50 which is 10 % of 500.(by removing last zero you will remain 10 % of the amount),, now 10 * 2 = 20 so multiply 50 with 2 to get 20 % of 500. Isn't it easy.

If your doing fractions divide the top by the bottom