If you want a lame excuse for not investing for your future, take your pick:

"I don't have any extra money to invest."

"I've got decades until retirement."

"Are you going to eat all your fries?"

What you're really saying, however, is: "I'm not interested in having an extra $5.6 million for my retirement. Pass the ketchup."

Oh, now you're listening?

I've played tough cop, concerned friend, and best shopping buddy, but now I get the picture: Money talks. So I'll step aside for a moment and let you powwow directly with the dinero.

Fun with math
Saving just $50 per month (about a buck seventy-five a day) comes to $600 per year -- and $6,000 in 10 years. Not bad, but if you invest that same $50 each month and it grows at the historical stock market average of about 11% per year, it'll amount to nearly $80,000 in 25 years.

How about a $40 weekly investment -- a little more than $2,000 a year -- into a company growing at an average rate of 13% per year? (You can cost-effectively invest small amounts of cash in companies from Pfizer (NYSE:PFE) to Ford (NYSE:F) to Coca-Cola (NYSE:KO) to Chico's (NYSE:CHS) via dividend reinvestment plans, or Drips.) How much pre-tax dough are we talking about? After 30 years, you'll have $610,322.

Oh, but you're interested in that $5.6 million mentioned earlier. You can get there in $10 increments. Let's say your Drip company grows at a rate of 13% per year over the next 60 years. Further, assume that you add $10 every week to that investment during that time period. How much pre-tax money will you have in 60 years?

You guessed it: $5,600,000.

I know what you're thinking: "I clicked on that headline, and all I got was a stinkin' 60-year example. Does it look like I can wait 60 years for the big payoff?" (Those readers who have an 8 p.m. bedtime are thinking: "Sweet! Mom! Dad! I need a glass of water and a stock!")

The point is, you can probably scrape up more than $10 a week and even come up with a few decent investing ideas that'll perform better than the stock market's average. (If not, tap one of our analysts for a few stock picks. You can ask for a small loan, too, but I haven't had much luck with that so far.) Toy with our savings calculators to see how your investing funds and time frame play out for your future.

The key ingredients to turning those fivers into five million are time, amount invested, and rate of return. The magic sauce is making the case for saving and investing so compelling that those old excuses for not doing so seem lame even to you.

More excuses to invest:

Dayana Yochim owns none of the companies mentioned in this article and prefers ketchup with her fries. Feast on the Fool's gourmet disclosure policy .