Calculating a Standard 15Percent Tip
Calculating a 15percent tip in your head may seem tricky, but here’s a, well, tip for those situations when you need to calculate that standard tip amount. And it works 100 percent of the time. In order to determine a 15percent tip, follow these steps:

Take the bill and figure 10 percent in your head.
Just move the decimal point one place to the left. For a $50.00 dinner, that’s $5.00.

Figure half of the amount created in Step 1.
Half of 10 percent is another 5 percent. In this case, you get $2.50.

Add the amounts from Steps 1 and 2.
Together they’re 15 percent of the bill. So $7.50 ($5.00 + $2.50) is a 15percent tip for a $50.00 dinner.
Many cellphones and smartphones have tip calculators, but the steps provided here can help you out in a pinch if you don’t have access to your phone for some reason.