Planning for retirement takes decades, and it's not easy to establish a nest egg worth hundreds of thousands of dollars or more. But even though many workers are woefully unprepared, others might actually be on track to retire early.

Early retirement is difficult to achieve, but not impossible. To retire in your 50s (or even earlier), you need smart savings habits and a good understanding of some of the challenges that come with early retirement. If these three signs sound familiar, you might be on the right path.

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1. You're saving more than you need to each month

One of the reasons early retirement is so challenging is that you need to save more money, and you have fewer years to do it. Especially as life expectancies continue to increase (a third of today's retirees can expect to live into their 90s or beyond, according to the Social Security Administration), you might end up spending close to half your life in retirement if you leave the workforce early. That means you'll need to supercharge your savings.

As you're planning for retirement (regardless of what age you want to do it), it's crucial to have a savings goal. One way to determine this is with a retirement calculator to estimate how much you'll need to have saved by the time you retire -- as well as what you should be saving each month to achieve that goal. Once you have your results, if you find you've been saving more than necessary each month, that's a good sign you'll end up with a solid stash at an earlier age.

Keep in mind, though, that this alone doesn't cover early retirement. Double-check your plan by recalculating your retirement number with your desired early retirement age. Your results will likely be different, but if you're still saving enough each month to reach your new goal, you're right on track.

2. You're in good health and have a plan for covering healthcare costs

Healthcare costs can quickly sabotage your retirement, but they can be even more taxing if you retire early. You won't have access to Medicare until age 65, so if you retire before that, you'll need to cover these expenses.

Anyone in poor health or facing chronic illness will likely have higher healthcare bills, which can quickly eat away at retirement savings. That's not to say you can't retire early if you're not in peak condition, but just know that health insurance may be more expensive than you think during the years leading up to Medicare eligibility. Even the healthiest retirees may end up paying hundreds of dollars per month in premiums and face sky-high deductibles, so if you expect to take many trips to the doctor or need expensive prescriptions, these costs can add up quickly.

Before you retire, figure out how you'll pay for healthcare, and estimate the best you can how much it will cost. Medicare isn't entirely free, either, so these costs won't go away once you turn 65. But the better idea you have of what healthcare will cost during your early and later years of retirement, the better you can budget for it.

3. You don't expect to rely on Social Security

Social Security benefits can help tremendously during retirement, but you're not eligible to start claiming until age 62, so if you plan to retire before then, you'll need to get by for at least a few years without them.

Also, claiming benefits at 62 means smaller checks than if you were to wait to claim until your full retirement age (FRA) -- which for those nearing retirement is either 66, 66 plus a few months, or 67, depending on the year you were born. These cuts can be significant, too; if your FRA is 67 and you claim at 62, your checks will be reduced by 30%. If these benefits will be a key in helping you afford an early retirement, claiming them early might throw a wrench into your plans.

Conversely, if you can live off a solid retirement fund until past your FRA, you can earn additional benefits each month you wait to claim. For instance, if your FRA is 67 and you claim at 70, you'll receive an extra 24% each month on top of your full amount for the rest of your life -- extra money that can go a long way.

Saving for a traditional retirement age is challenging enough; retiring early requires even more hard work. But it can be done if you save a good chunk of money each month, you have a plan to cover (potentially expensive) healthcare costs, and you can afford to wait a few years for Social Security benefits.