Thanks to Stephen Gilbert, who found this outstanding resource in the New York Times. 

It lets you calculate the effect of, say, switching from Starbucks to office-brewed coffee (or bringing your own peanut butter and honey sandwiches to work with you instead of buying them off the cart).  Say you buy one $3.50 cup of coffee a day and could get it for 50 cents from the office vending machine or brewing it yourself. 

I’m not saying you should do this – or save another $3 a day by not buying cigarettes or whatever. 

But if you did do this, starting now, at age 49, say . . . and if you could invest your savings at 6% over inflation, which is no slam dunk but not nuts, either . . . by the time you were 84 (with another 10 or 15 good years ahead of you, let us pray), you’d have an extra $83,000.

Or $122,000, if we’re talking $3 a day on cigarettes, because with the coffee I was figuring 5 days a week, 50 weeks a year.  With the cigs, we’re talking 365.25 days a year.

If you’re 18 today and saved the same $3 a day, by the time you’re 65, with the same 6% assumption, we’re up to $264,000. 

Of course, if you’re 18, you’re thinking you’ll never be 65.  But actually the chances are that you will be – with an an extra $264,000 after tax in today’s dollars in your Roth IRA, for being a bit frugal.

It’s cheating – but fun – to assume more than 6% above inflation, but it’s not impossible, either.  So if we go wild and assume 7% instead, the $264,000 jumps to $360,000.

And remember, this is still just on $3.  You could double that if you found a second way to save $3 a day – say by buying one fewer gallon of gas a day by (in the short run) driving more carefully and (in the long run) switching to a car that got better mileage.

Hugh Chou has a whole range of other frugality calculators.  Play with them, and then set up that Roth IRA if you don’t already have one.

There’s tons of good and amusing stuff on his site to ponder.