I always ignored my dad's money advice until I watched him use a 4-step strategy to retire at 55

• I ignored my Dad's advice about saving money and investing until I saw him retire a decade before his peers.
• Now, he and my stepmom get to enjoy retirement while they're young and healthy, and they spend their time traveling the globe.
• I asked how they did it, and they explained their retirement plan. It involved living below their means, investing everything in a combination of retirement accounts, stocks, bonds, and rental properties, and coming up with a back-up plan.
• Need help with your own retirement plan? SmartAsset's free tool can find a financial planner near you »

As a child, there's no joy quite like opening a birthday card and seeing crisp dollar bills fall out.

Growing up, my Dad tried to convince me that this cash, when saved, symbolized opportunity for my future self. I'd hold my birthday money up to the light to see the watermark and try to picture my future self enjoying this money, but all I could see was my current self enjoying 7/11 Slurpees, top-ups for my pre-paid cell phone, and band tee shirts.

When I got my first job in high school, my Dad printed out an article about the power of compound interest and put it in my purse with a note: "Start investing early Lizzie." My money left my bank account almost as soon as it entered that summer, and not because it was being funneled into a retirement account.

Even after I graduated college and got "grown up jobs," I didn't start saving. I contributed to my 401(k) for a while, only to empty it when I quit my job and use the money to road trip around the US.

I just never quite understood the point of letting my money sit around in someone else's pocket for decades until, hopefully, I could one day spend it - not when there were so many things I could spend it on now.

Then I watched my Dad retire at least a decade before many of his peers, and my entire perspective changed. My stepmom retired even younger, after my Dad convinced her to join him in his plan for early retirement.

Hoping it wasn't too late for me to get my finances on track, I asked them how they did it.

How my parents retired early

My Dad had always planned to retire early. He was frugal and highly practical growing up⁠ - my sister and I ate a lot of $0.50 frozen pot pies and didn't get new sneakers until there were holes in our current ones. He was generous with stuff that mattered, though, like educational opportunities that could set us up for a better future. But education is an investment; shoes are not. He understood that money invested usually provides more value to your life, in the long-run, than money spent. You invest first, then you spend.

My stepmom, on the other hand, never had plans to retire early until she started dating my Dad. When he told my her he wanted to retire by 50, she looked at him incredulously. "I told him, there's no freaking way," she recalled to me.

She played along anyway. As it turns out, his goal wasn't so unrealistic.

My Dad would have been on track to retire by 50, which was a stretch goal, if it weren't for the 2008 recession, which decimated his retirement accounts. However, he was able to eventually recover and retire at 55. My stepmom retired at 49.

Both my Dad and stepmom worked in sales and marketing for a high tech company by way of degrees in electrical engineering, so it's worth stating up-front that they both earned salaries that most would consider more than comfortable.

Regardless, most people - my non-engineer self included - can apply the advice they gave me.

1. Set a goal, create a budget, and track your progress

Setting clear goals and tracking your progress will make all the difference. It wasn't until my stepmom checked in on their progress and saw their money growing according to plan that she started to believe they could retire early.

"I realized it was real," she told me. "When you make saving a priority, retirement becomes possible. Money makes more money, and it makes it surprisingly quick."

The first thing they did was figure out exactly how much money they'd need to comfortably retire when my dad hit 50 and live off that money well into their 90s. Their retirement budget included a salary equal to their pre-retirement pay and line-item expenses for things like healthcare.

After creating a retirement budget, they worked backward to figure out how much money they'd need to save each year to get there by age 50, taking into account the expected rate of return on their investments. Then, they cut spending and invested all of their extra earnings to meet that goal.

They checked in with their budget regularly and did a full progress assessment every six months. Eventually, they started meeting with a financial adviser for these biannual check-ins, and they've continued them in retirement to make sure they're still where they need to be.

2. Avoid lifestyle inflation

Lifestyle inflation, or increasing your cost of living every time your income increases, is one of the most insidious ways to destroy a retirement plan. It often lands folks in debt.

For my parents, living below their means was essential to retiring early. They invested at least half of any raise. My Dad's bonuses at work were invested in rental properties that could generate income. When they got married, my parents bought a house that was priced at half of what they could actually afford.

They also didn't go overboard on cars. Our whole family has always driven Hondas, and my parents drive a car until it stops running. They did get all of us kids cars, but we got old, used cars for a couple grand - mine was a 1990 Acura Integra - and paid for them in cash.

3. Invest aggressively ... and diversify

Like most people, a 401(k) was central to my parents' retirement plan. They took full advantage of employer matching from the start and worked up to maxing their 401(k)s as early as possible. My stepmom also runs a consulting business, so she opened a SEP-IRA, which is an option for folks who are self-employed.

Because they wanted to retire early, my parents had to have other investments they could rely on for retirement income. Retirement accounts, like a 401(k) or SEP IRA, shouldn't be touched until you've actually reached retirement age (59 ½). If you withdraw funds early, you'll incur a hefty penalty.

So, my parents also invested in stocks, bonds, and rental properties to provide income until they turn 59 ½.

After the recession, my parents bought foreclosed houses in cash at extremely low prices. They renovated the houses, doing all the work themselves to save money, and then rented them out.

These properties now serve as income generators for the early years of their retirement as well as a safety net, as they can be sold off one by one. My parents know that they could weather a 30% cut on what they live off of, thanks to the properties, and still be fine.

In addition to rental income, they've set up a bond ladder to live off of in the short-term. Each year for the next four or five years, they have bonds maturing that provide them with income.

4. Consider a part-time back-up plan for income

My stepmom is younger than my Dad, so she planned to work a little longer. However, rather than continue with the company where they'd both worked, she decided to start her own consulting business online that would help her transition to full-time retirement.

My stepmom still does consulting work on the side for "fun money." They've used this consulting income to go on a safari in South Africa, take their parents to Germany, and throw a big anniversary celebration with the whole family in St. Thomas, where they now live part of the year.

If anything ever happened to one of their income sources, they could always lean on my stepmom's consulting.

Why early retirement was important to my parents

A lot of people my age (20s and early 30s) can't envision retiring at all, let alone early, so it surprised me that my Dad had been planning early retirement since he was my age. I asked if any life experiences or lessons had helped him gain that foresight at such a young age.

"I think it was your Dad's mom dying young and Alzheimer's running in the family," my stepmom offered. "He felt like he really wanted, while he was in good health, to have his own life."

My Dad agreed. "That was part of it," he said. He also brought up my aunt, his sister, who died of cancer. When he saw how quickly she went from perfectly healthy to very sick, they doubled down on their plan to retire. "I could've kept working, but when your aunt passed within six months of being diagnosed I said, 'Why are we waiting?' I just wanted the freedom to do what we wanted when we wanted."

"We enjoyed [our work] but it was like, this isn't what I am," my stepmom added. "This isn't what I want my whole life to be."

Now, they spend almost half the year in the Caribbean, learning how to play guitar, going on sailing trips, and doing volunteer work. They've traveled all over the globe, spending several months road tripping to the best US national parks, exploring Europe, spotting wildlife in South Africa, cruising the Panama Canal, and visiting relatives.

Watching them, I've learned that saving money is the opposite of letting it sit around collecting dust. If invested properly, that money grows indefinitely, and it will probably do a lot more for me in the long-run than spending it would.

My stepmom framed it in a way that really resonated with me. "It's not your money, it's your future self's money," she said. Think of saving and investing as a form of self-care for your future self. Your future self will thank you.

SmartAsset's free tool can find a financial planner near you to help create your own plan for retirement »

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