Kristina Jonathan, an Atlanta-based digital-marketing consultant, has no interest in keeping up with the proverbial Joneses.
For years Johnson, 38, has lived frugally, investing in real estate, maximizing her 401(k) plan savings and reducing expenses.
By Johnson’s own account, she has amassed a net worth of nearly $1 million and figures that she is a couple years away from being able to retire if she maintains a modest lifestyle and lives in a house that she now owns outright.
She wants to continue to work on her own terms by cherry-picking projects that interest her.
Read More Is Gen Y ready for retirement?
“For a long time, I was the only voice in the crowd,” Jonathan said, referring to scrimping, saving and paying off debt in hopes of attaining financial independence.
“My peers were getting married, spending a lot on weddings, buying big houses, maybe a boat and two to three cars,” she said.
Tricky but doable
Financial advisors say that it is possible, though difficult, for the average American worker to retire by 40. Some people who actually do it are part of the so-called “early retirement extreme” movement, populated by those who live frugally in order to save significant portions of their income and often blog about it.
Some, like Joe Udo of Portland, Oregon, live below their means and strive to create investment portfolios that will someday generate enough income to cover their expenses.
Read More New retirement reality tests savers
Udo, 40, left a high-pressure job as an engineer at Intel two years ago and now spends his time blogging, caring for his young child and managing his investments.
He and his wife, who works full time, live on half their yearly income, even though they already have a net worth of more than $1 million, according to Udo.
To save money, they share one car, rarely dine out and scrimp in other ways.
“There is the early retirement extreme movement, and then there are people who don’t ever want to stop working entirely, because they enjoy what they do,” said Erik Carter, a certified financial planner and senior resident planner at Financial Finesse.
Read More Future retirees get “F” for know-how
Many of those who retire well before their 60s want the freedom to devote their time to such things as charitable work, traveling or writing the “great American novel.”
In fact, those who have a clear picture of how they plan to spend their time during retirement are generally more motivated than those who don’t when it comes to making necessary changes, such as slashing expenses, Carter said.
They are also in a better position to gauge how much money they will likely need during retirement, he said.
Most people will need 70 percent to 80 percent of their pre-retirement income in order to maintain their standard of living during retirement, by which time they will have ideally paid off home mortgages and any other major debt, according to advisors.
Read More Allocation key in retirement
Those who aim to retire early need to consider that their spending habits can change dramatically over time, said F. Reid Hartsfield, a certified financial planner and financial planning strategist at BB&T Wealth Management.
For instance, paying to send a child to college can undermine retirement savings plans, he said.
Many people underestimate how much money they will need, because spending on leisure activities, such as travel, often increases immediately after retirement, said Douglas Kobak, a certified financial planner and senior advisor and principal with Main Line Group Wealth Management.
For those who retire in their 60s, spending on leisure activities tends to trail off after a decade or so, but that is when health-care costs generally pick up, he said.
Read More Retirement years not so golden
Passage of the Affordable Care Act in 2010 actually made it more feasible for Americans to retire early, particularly because insurers can no longer charge higher rates to those with preexisting conditions, and those with low taxable incomes may qualify for subsidies, regardless of their net worth, Carter said.
Still, those who retire in their 40s will have to wait decades, until at least 62, before they are eligible for Social Security benefits, and they are likely to collect less in benefits than Americans who pay into the system for a longer time. They may also need their money to last for 40 to 50 years.
Many advisors adhere to the so-called 4 percent (plus inflation) rule when it comes to determining how much clients should be able to withdraw each year from retirement savings. But that rule is based on the assumption that a retirement portfolio should last three decades.
Those who hope to retire in their 40s should use a 3 percent withdrawal rate so that their retirement portfolio lasts for as long as 60 years, Carter said.
Read More Retirees launch encore careers
Of course, anticipated rates of return and inflation are wild cards. Taxes are also a big consideration for early retirees, given that many people save most of their money in retirement accounts, which levy penalties for withdrawals before a certain age.
“If you are going to live for 50 years in retirement, that puts an onerous amount of pressure on your portfolio to keep pace with inflation,” said Gustavo Vega, a certified financial planner and managing director at Vega & Oprandi Wealth Partners.
Advisors say even those who win the lottery, sell businesses for a handsome price or make millions as professional athletes can find themselves sweating it out when it comes to retirement.
Why? Those sitting on a pile of money often end up investing in business ventures that may not pay off, or they may refuse to rein in their spending and/or fall victim to bad investment advice.
Read More 401(k) cash in pensions? No way!
What’s more, many people struggle with a loss of identity if they haven’t thought about how to find purpose once they walk away from a business or career, said Karl Frank, a certified financial planner and president of A&I Financial Services.
“We lose our relationships when we retire,” Frank said. “So this isn’t strictly a financial conversation.”