For consistent 15 percent tipsters living in municipalities with a 7.5 percent dining tax, generating the perfect 15 percent tip is as simple as doubling the tax. If that's not you, Oh Arithmetic-Challenged One, you've got a bum deal. (See below for a quick computational technique.)
It's for this set, and for diners who frequently split a bill, that Ilium Software developed Tipster. The free, simple app for Palm, Windows Mobile smartphone and Pocket PC hurriedly computes your tax and total.
Tipster calculates tax in 5 percent increments up to 30 percent, and can evenly split the amount owed among diners (up to ten,) tip included. Working out how much four people should pay on an $86.52 bill with a 20 percent tip becomes instant and headache-free. Just don't try anything funny, like tipping 18 percent.
Math-addled? An easy way to compute 15 percent tip.
1.) Look at the total bill: $20.51 (or euros, pesos, etc.)
2.) Take the first three digits (in bills under $1,000), and mentally add a decimal point after the first digit.*: $20.51 --> $2.05. That's 10 percent. Let's round down to $2.00.
3.) Halve that to get 5 percent: $1.00.
4.) Add both calculations to reach 15 percent: $3.00
*To calculate 10 percent in bills under $10, take the first two digits and make them cents: $7.50 --> 75 cents. To calculate 10 percent in bills over $1,000, add the decimal point after the first three digits: $1,150 --> $115.