In December 2016, Steve Adcock left his career in information technology at age 35. His wife, Courtney, joined him in early retirement in April 2017.
Adcock, now 36, is the first to tell you that saving money doesn't get you rich — and it isn't "the magic sauce to early retirement" — but it still helps. He and Courtney set aside up to 70 percent of their combined income, which ranged from $200,000 to $230,000 a year.
If you want to bank half your income or more, start the way the Adcocks did: Track your spending.
"We know exactly what we bring in and exactly what we spend — and on what, " writes Adcock, who wasn't always thrifty and only saved "the bare minimum" in his 20s. "Knowing where our money goes is critical to maximizing our savings and pinpointing where we could probably cut back."
They're far from the only early retirees who track their spending. The strategy worked for Justin and Kaisorn McCurry, for example, who banked more than $1 million in a decade to retire in their 30s.
"You have to know what you are spending before you can plan your retirement budget," says Justin. Plus, "knowing how you spend lets you determine whether you get value for your dollars, and where you might be able to focus efforts to reduce expenses further."
If you need extra motivation, think about how many hours of your life it took to save up the money you're about to spend to make a purchase. Ask yourself "if another year of working for a living is worth that shiny new thing," says Adcock.
This mentality helped him cut back on his biggest vice: dining out.
"We only went out to eat once or twice a month, and I love going out to eat, " Adcock tells CNBC Make It. "But the way we thought about it was: Is this spending worth another month of working? And more times than not, the answer was, 'Oh, heck no.' It made it really easy to say no to certain things."
At the end of the day, he says, "I don't like restaurants enough to work for the next 30 years of my life."
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