We often look at the price tag, but the true cost of an item is the price divided by the number of times we actually use it. A $100 pair of shoes worn 100 times costs $1 per use. A $20 gadget used once costs $20 per use.

This tool helps you evaluate impulse purchases by forcing you to estimate their utility and longevity. If the "Cost per Use" is higher than a cup of coffee, you might want to think twice.