'A millionaire is made ten bucks at a time': A personal finance expert who retired at the age of 30 shares his best investment, life, and spending advice for anyone looking to exit the 'rat race'

• Peter Adeney - the author of the renowned Mr. Money Mustache blog - is almost 15 years into his retirement at age 45.
• He credits a voracious focus on saving and investing, frugality, and incrementalism for his financial independence.
• He also shares why every single financial decision counts.
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When Monday morning rolls around, it's safe to say that most 45-year-olds are waking up to alarm clocks and gearing up to tackle another grueling week at work.

Laden with debt and struggling to make ends meet, a majority of these workers are living paycheck to paycheck just to keep the lights on. In fact, in 2017 it was estimated that 78% of all workers are spending everything they earn.

And then there's Peter Adeney - the author of the widely recognized Mr. Money Mustache blog - whose life is anything but typical.

Adeney has been retired for 15 years - and he's only 45 years old. What's more, he's self-made. No rich parents. No windfall inheritance. No bag of cash falling from the sky.

So how could he possibly manage to retire at an age where most are just settling into their careers?

The answer is simple. It starts with a frugal, incremental mindset and moves to a voracious focus on saving and investing. He thinks that anyone who employs a similar methodology is destined for success as well.

"I can very clearly imagine what a powerless and trapped feeling people must have, to be my age and still mostly broke, with kids and a mortgage, almost 25 years into the cubicle grind with no end in sight," he said in an exclusive interview with Business Insider.

Early on, Adeney realized that the keeping-up-with-the-Joneses mindset was more likely to keep him broke than happy. Instead of surrounding himself with material items, he started focusing on increasing his life satisfaction while spending less. It's a key component of proper financial management - and a crucial part of getting out of the "rat race" maze.

"Every time you contemplate buying a new pair of shoes or a fancy bottle of wine or a shiny new pickup truck, you are building the walls of that maze a little higher and thicker," he said. "Every time you learn a new skill or solve a problem without spending too much money or get outside for a walk, you are tearing those same walls down."

Reining in spending habits, and an ETF recommendation

Adeney makes an important distinction here. Being mindful of how your spending habits affect your financial future is not something a lot of individuals tend to think about on a day-to-day basis. But he focuses on this notion incessantly. To him, each decision either moves you closer or further away from financial freedom - and they compound directionally.

He continued: "Every single decision counts, because little decisions become ten dollar bills, and one of my favorite slogans is that you get out of debt ten bucks at a time, and that a millionaire is made ten bucks at a time."

Although Adeney admits he takes this notion a little bit further than most, he's quick to note that it doesn't have to be an all or nothing approach. Think of it as steps forward and steps back.

Once your spending is in check, you can focus on saving.

"When you streamline your spending, whether it means giving up drinks out on the town or driving less or moving closer to work and a hundred other decisions, you can quickly go from spending 100% (or more) of your income, to saving at least half," he said. "At this point, just take half of your annual salary (say $25,000 to use a typical number) and imagine paying off $25,000 of your debt or amassing that amount of investments every year."

Those slight, incremental spending and saving lifestyle changes add up fast - and this enabled Adeney to start socking away any spare cash he had into index fund ETFs. His personal favorite - and choice he recommends - is the low-cost Vanguard Total Stock Market Index Fund ETF (VTI).

Before he knew it, he had amassed enough cash to retire - a full 35 years before most.

Now, he lives comfortably off of that investment income - and plans on doing so for the rest of his life.

"If you do it right, financial independence is just the whole life equivalent of physical fitness and health. So it's 100% upside with no downsides at all," he concluded.