You know you've done this. You are at a restaurant in the land where it is called soccer, and the bill arrives. If you have cash, it is easy to toss some on the table and flee. But with a credit card tip, you are forced to do math. You hesitate. You want the total to be an even dollar amount -- who doesn't? You also want to have control over the tip.
But most of all, you want to send a message. Who are you at the table with? Can you envision any scenario in which you would wish to appear clumsy, unsure of yourself, slow, or greedy to the person opposite you? You can be charming as a prince, but if you spend 30 pathetic seconds calculating an 8% tip, your date will notice, and this person of indeterminate or irrelevant gender will not be impressed. Neither will your children, your parents, your co-workers, or your friends. Even if the service is terrible, you should be able to be confident in your decision to undertip. Don't be afraid. Sink your sword swiftly into the disposable income of your server.
This brings me to the point. When I started to wait tables, it took me ages to divide by ten, then divide in half, then add (yes, thank you Simulacron3, that is exactly what I was talking about), to determine if I had done a good job at that table or not. So I figured out a quicker way to get an idea of 15%.
100 divided by 15 is 6 and two thirds. So the tip for a bill should be a little more than one seventh of the check.
Does dividing by seven sound hard? It isn't. You know the multiples of seven. Assuming you want to tip in the 15% range:
For checks around $7, tip about a dollar.
For checks around $14, tip about $2
For checks around $21, tip about $3
For checks around $28, tip about $4
For checks around $35, tip about $5
You get the idea. Remember to round up. The change should take care of it -- if the check is $27.36, and you want to tip in the 15% range, write down 4, then toss on a 64, and you now have made a $4.64 tip which is between 16% and 17%. That is a good, healthy, decent, American tip to leave for standard service. And because you noticed that 27 was almost 28, you were able to write down that tip in the blink of an eye, with a strong, confident, attractive flourish of the pen you are borrowing from your server. Good for you.
Addendum: I have never met anyone in my entire life who thought this method was a good idea. Your mileage may vary, you can divide by 10 and then 2 if you want, I personally don't care. If it's easier for you, go ahead. I have no doubts that people will read this node and recoil in revulsion as though I were suggesting an alternate way to eat the food, because I have seen it happen in real life. "But what if the bill is halfway between multiples of 7, like $31.89?" you might say. Seriously, folks, 7 is not that large of a number, and the difference between a 13% and 16% tip is not that big. $31.89 is close to 35, so leave $5.11 for a ~15% tip for decent service. That's not so hard, now, is it?
And I shouldn't have to say this, but I suppose I must. To increase the tip, add a dollar. To decrease it, take away a dollar. Bingo.
At the very least, consider this: 93% of communication is non-verbal, and I know that because I saw it on Seinfeld once, I think. Or maybe that's wrong. I don't know. Anyway, be advised that you are sending messages when you tip to many people -- the server learns about themself, the server learns about you, the manager learns about the server's competency, and perhaps most importantly, your companions learn about you. Hide all you want, but they will find out if you are a good tipper or not. Being comfortable and secure in your decision about tipping can affect their perception. Even if you don't like 7, you hate 7, and you wish 7 would curl up and die, figure out what works for you and stick to it. Even if you never notice, it will reflect positively on you.
The purpose of this node is not to discuss the pros and cons of the tipping system in the US. If you are interested in that debate, I direct you to why you should tip waitresses. If you are interested in my opinion, ccunning lays it out.