Early retirement sounds great on paper, but the reality isn't always as rosy. A longer retirement means stretching your savings further and more years of unexpected expenses to worry about. It takes a lot of planning -- and money -- to pull it off.

If you have your eye on an early retirement date, aim to do these three things before you tender your resignation.

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1. Have a safe withdrawal strategy

No matter when you retire, you should have a plan for how much you'll withdraw from your accounts each year to help your money last. One popular strategy is the 4% rule: You withdraw 4% of your total savings in the first year of your retirement and adjust this amount for inflation in each subsequent year.

But some people don't like how rigid this system is, while others fear it could cause them to drain their savings too quickly. You might choose a lower withdrawal rate or create your own custom withdrawal strategy.

If you plan to travel a lot in the early years of your retirement, for example, you could take a higher withdrawal rate in these years. Then, you can decrease your withdrawals as you get older and remain closer to home.

If you're retiring before 59 1/2, you'll have an additional hurdle to contend with. Most retirement accounts charge you a 10% early withdrawal penalty if you take money out before that age, so you'll need to find a way around this. 

You could rely upon Roth contributions in your early years -- you can withdraw these tax-free at any age. Or you could use the Rule of 55 to help you tap some of your 401(k) funds early.

You can also save money in a taxable brokerage account. These aren't technically retirement accounts, so you can invest as much as you want and withdraw the funds at any age.

2. Have a plan for Social Security

You don't become eligible for Social Security until you're 62, so if you retire before this age, you must cover your expenses without it. And just because you could sign up at 62 doesn't mean that's the best decision for you.

You have to wait until your full retirement age (FRA) -- 66 to 67, depending on your birth year -- if you want the full benefit you've earned based on your work history. Claiming earlier than this will give you more years of checks, but each one will be smaller. You only get 70% of your full benefit per check if you sign up right away at 62 and your FRA is 67, or 75% if your FRA is 66. And that reduction is permanent.

Conversely, delaying benefits beyond your FRA slowly grows your checks until you reach your maximum benefit at 70. That's 124% of your full benefit per check if your FRA is 67 or 132% if your FRA is 66. Waiting to claim could result in a larger lifetime benefit if you live into your 80s or beyond, but it also means you're getting no help with your expenses until then.

The right claiming age depends on your guess on life expectancy and your finances. You can create a my Social Security account and use the calculator it provides to estimate how much you'll get at various ages, to help you choose the starting age that makes the most sense for your retirement plan.

3. Have a backup plan

Retirement plans can always hit a snag. You might fall ill or be injured and rack up medical bills. Or your investments might not do as well as hoped, forcing you to drain your savings faster than expected. For any situations like these, you need a fallback position.

Be ready to return to work full or part time for a while to rebuild your savings or allow your portfolio to recover. Or be prepared to rethink your budget, eliminating some discretionary purchases. 

Once you think about how you'll handle this worst-case scenario, check at least annually in retirement to see how you're doing. If you worry you're getting off track, you'll have a backup plan.