You Could Become a Millionaire in 33 Years for the Cost of 1 Restaurant Lunch Per Day. Here's How.

Is your daily lunchtime routine preventing you from becoming a millionaire? As crazy as it might sound, this very well could be the case for many Americans. Although convenience and perhaps a bit of socializing also factor into the decision of what and where to eat for your midday meal, given enough time, making this choice over a simpler and more cost-effective alternative could mean the difference between a comfortable retirement and a financially strained one.

Here's the math to prove it.

Where to invest $1,000 right now? Our analyst team just revealed what they believe are the 10 best stocks to buy right now. Learn More »

The underlying assumptions apply to everyone

Before getting to the number-crunching, let's first lay out the underlying assumptions of my model.

First, let's assume that the money you're not going to spend on a typical restaurant's lunch is instead going to be invested in the stock market, which over time returns an average of 10% per year. Sure, some years are better, while other years are worse. Every three to four years stocks even lose ground. Over the course of three decades though, odds are good the market will dish out its long-term average annual gain of 10%.

Second, let's assume you're going to be investing this money in an individual retirement account, or IRA. This allows the money to grow tax-free for at least as long as you leave it in the account.

Third, we're going to assume you put this extra cash into the IRA and invest it on a monthly basis. Doing it daily or even weekly would be needlessly busy, but waiting longer than a month to put it to work leaves too much money on the table.

And fourth, let's assume the average restaurant lunch will cost on the order of $15 per meal.

Image source: Getty Images.

Some people might dispute that figure, and understandably so. Although it's not a particularly big meal, for example, McDonald's offers a small burger, fries, and drink combo for $5. A small sandwich with chips and a drink sells for about $7 at most Subway restaurants.

That's not every meal you're going to eat though. Even a relatively light lunch at, say, Applebee's is going to start at $10 and easily approach $20 after adding a beverage and tip.

So, $15 per day is a reasonably accurate average figure to use.

That still doesn't seem like much, but this might change your mind. That $15 per day is $75 per five-day workweek, $325 per month, or $3,900 per year. That amount could really matter over time if it's tucked away in an investment with an average annual return of 10%.

The graphic below tells the tale. Assuming you're putting aside $325 every month and achieving average gains on it, after 33 years you should have just a tad more than $1 million.

Data source: Calculator.net. Chart by author.

Notice that things really take off around two-thirds of the way through the time frame in question. That's when the gains on your investments start to become bigger than your annual contribution of new money. You just have to be patient en route to that point.

This is how it's (almost) always done

It's a simplistic mathematical model, of course, and doesn't necessarily tell the entire story. For instance, even if you're not eating a $15 lunch every day, you're still paying for lunch somehow. Groceries aren't exactly cheap either!

Also bear in mind that $1 million won't be worth nearly as much 33 years from now as it is today. Assuming an average inflation rate of 3%, that's only going to be worth about $400,000 in today's dollars.

You'll also be earning more money in the future, and the typical lunch will also cost more. That's how inflation works.

Still, the chief takeaway is that the seemingly small things aren't actually all that small. They add up over time, for better and for worse. That's why even if you can't save $15 on lunch every single day, it might be worth occasionally cutting out that one big dinner splurge every week, or perhaps canceling that streaming subscription you don't use all that often anyway. A smaller car payment or a little less spending on clothing could save you on the order of $300 per month as well, and wouldn't dramatically crimp your lifestyle.

And for the record, this is how most self-made investment millionaires did it. The bulk of them never stumbled across a once-in-a-lifetime kind of opportunity that turned a tiny investment into a fortune. Most of them got there just by being disciplined enough to take the smallest of baby steps over and over again... even when it wasn't comfortable to do so.

That's great though. It means you can do the same even if you don't have a ton of money left over at the end of the month. The key is consistently doing what you can with what you've got, and perhaps making the smallest of lifestyle sacrifices along the way. It's worth it in the end.

The $23,760 Social Security bonus most retirees completely overlook

If you're like most Americans, you're a few years (or more) behind on your retirement savings. But a handful of little-known "Social Security secrets" could help ensure a boost in your retirement income.

One easy trick could pay you as much as $23,760 more... each year! Once you learn how to maximize your Social Security benefits, we think you could retire confidently with the peace of mind we're all after. Join Stock Advisor to learn more about these strategies.

View the "Social Security secrets" »

James Brumley has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.