The lunch savings calculator at soundmoney.publicradio.org lets you calculate what you save by bringing a lunch instead of eating out. You can adjust the average cost of going out for lunch, the cost of your brown-bag lunch and the frequency you eat out.

For example:

Cost of going out for lunch

$7

Cost of a brown-bag lunch

$3

Two-year savings from eating a bag lunch 20 times a month, at a 5 percent rate of return

$2,021