Lately I’ve found myself using more and more financial rules of thumb. A rule of thumb is a general guideline, an easy way to approximate a value quickly. It’s not meant to be completely accurate. On a whim this weekend, I gathered together many of the general rules I’ve been using, as well as several others I found online. Thanks to those who follow me on Twitter, who also contributed suggestions.

For example, @FourPillars wrote, “I hate rules of thumb — they are a poor substitute for proper analysis.” He’s right, of course. Careful analysis always yields the best results. (And there are times when you need the advice of a financial professional.) All the same, it’s often convenient to get a quick estimate of financial numbers. For those situations, it’s helpful to know guidelines like the ones I’ve listed below.