Inside the lives of surprisingly frugal millionaires and billionaires, from businessmen like Warren Buffett and Richard Branson to A-list celebs like Jay Leno and Jennifer Lawrence

• Frugality is one of the key characteristics of wealth, according to a researcher who studied more than 600 millionaires.
• Those who commit to saving, spending less, and sticking to a budget are more likely to become millionaires, she said.
• Many of the richest people, including Warren Buffett and Richard Branson, have surprisingly frugal habits.

Many millionaires and billionaires have something in common aside from having high net worths: They're frugal.

It's this characteristic that helped them become rich in the first place, according to Sarah Stanley Fallaw, director of research for the Affluent Market Institute. She coauthored "The Next Millionaire Next Door: Enduring Strategies for Building Wealth," in which she surveyed more than 600 millionaires in America.

To identify characteristics that are the most predictive of net worth, Stanley Fallaw conducted two studies that included a group of individuals with net worths ranging from $100,000 to $1 million and a group of high- and ultra-high-net-worth individuals.

She found that six behaviors, which she called "wealth factors," are related to net-worth potential, regardless of age or income. One of those is frugality — a commitment to saving, spending less, and sticking to a budget.

That's not surprising when you consider the habits of some of the richest people: Warren Buffett is notoriously frugal, and Richard Branson has previously said that displays of wealth embarrass him. The same extends to some A-list celebrities who rake in millions for their movies and TV appearances.

Here's a look inside the lives of some famously frugal millionaires and billionaires.

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Sarah Stanley Fallaw, director of research for the Affluent Market Institute, studied more than 600 millionaires for her book, "The Next Millionaire Next Door: Enduring Strategies for Building Wealth."

She found that six behaviors, which she called "wealth factors," are related to net-worth potential, regardless of age or income.

Source: "The Next Millionaire Next Door"

One of those factors, frugality, came up several times during Stanley Fallaw's research — many of the millionaires she interviewed stressed the freedom that comes with spending below their means.

Source: "The Next Millionaire Next Door"