<h2>Divide By Six</h2> This one is simple, but I'm surprised that not enough people know it. My tip secret to divide the bill total by six.
Others use shortcuts like "twice tax", but that works out to over 18% now. Still a decent baseline to round up or down from. Another shortcut is "divide by ten then add half again". Divide by six is equivalent to 16.6%. Let's do a few tests to see what is easiest...
The bill is $24.52. Divide by six gives you $4 pretty quickly. Divide by ten and half again is $2.45 then what's half of that ... ok $1.20. $2.45 + $1.20 is $3.65. That was a lot more work!
The bill is $125. Divide by six gives you "Around $20 or $21". Divide by ten and half again is $12.50 plus $6.25, that gets us close to $19. But how much more effort was that?
<h2>Credit Card Whole Dollars</h2> WTF is up with people who do all this subtraction when calculating a tip so that the total charged to their credit card is a whole dollar amount? I mean really people -- what are you trying to accomplish? Do you keep a running total in your head -- to the nearest PENNY -- of your credit card? Then the poor server has to do all kinds of penny-precise math and finding of small change on account of your obsession with zeroes. REALLY!