Calculate a tip or gratuity and get the total amount to pay. Enter your meal or dinner cost along with the tip percentage. If you are splitting the cost at a restaurant among several people you can divide by the number of people to get the total cost each. Optionally round the results to dollars.
Tip = Cost * 0.xx
Total including Tip = Cost * 1.xx
where xx = the percent tip you want to leave.
How to calculate a tip on a calculator
To calculate a gratuity or tip on any calculator it is a simple multiplication. In general, the tip amount is the cost times 0.xx and your total including tip, is the cost times 1.xx where xx = the percent you want to leave. If you want to leave a 20% tip, multiply the cost by 0.20 to get the tip amount or multiply the cost by 1.20 to get the total including tip. If you want to leave a 18% tip, multiply the cost by 0.18 to get the tip amount or multiply the cost by 1.18 to get the total including tip.
Let's say you and a friend had dinner that cost $26.50. You had good service and want to leave an 18% gratuity. Put the percentage in decimal form (0.18) then multiply the cost by this number.
26.50 * 0.18 = 4.77. So your tip is $4.77.
An easy way to get the total amount, dinner plus tip, is to multiply the total by 1.18. 26.50 * 1.18 = 31.27. This works mathematically because you want to know your original cost plus the tip which is written as 26.50 + (26.50 * 0.18) = ? Factoring out the 26.50 from this equation you get 26.50 * (1 + 0.18) = 26.50 * 1.18.
How to calculate a tip in your head
You can get a good approximation of a tip by doing it in your head this way.
You can find 10% of your bill by moving the decimal one place to the left. If 26.50 is 100% then 10% is 2.65. Since 20% is 2 times 10%, 20% of the bill is 2.65 + 2.65 = 5.30. Now you know the tip you could leave ranging from poor to good, $2.65 to $5.30. To find 15%, halfway in between, we know 15% is 10% plus 1/2 of 10% (5%). 2.65 plus about 1.30 is 3.95.
Now you have
10% is 2.65 - by moving decimal 1 place left
15% is 3.95 - 10% + 1/2 of 10%
20% is 5.30 - 10% * 2
This is plenty of information to make a good guess at the tip amount you should leave. If you decide on about 18%, 4.50 to 5.00 would be a safe guess.