As someone with a bunch of hobbies I never seem to have enough time for, I totally get the appeal of the Financial Independence, Retire Early (FIRE) movement. You save half or more of your income, live frugally, and invest as much as you can, and then you retire in your 30s or 40s while most of your friends are still slaving away at their jobs for another 20 or 30 years. Sounds great, right?

But despite the obvious appeal, I'm not actually a FIRE movement follower, in part because I'm leery of all the variables involved. Retirement is unpredictable no matter how long it lasts, and the longer your retirement, the more unpredictable it is.

That doesn't mean the FIRE movement can't work. There are plenty of people who prove that it can. But you need to be prepared for some of the variables you may encounter if you'd like to stay retired for the rest of your life. Here are three questions all FIRE movement participants should ask themselves before they retire.

Woman looking at papers, laptop, and calculator

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1. How will I handle a financial emergency in retirement?

Most FIRE movement participants determine their FIRE number -- how much they need to save in order to retire -- by multiplying their monthly expenses by 12 to determine their annual expenses and then multiplying this by 25. So if you spend about $3,333 per month, that adds up to $40,000 per year, which means your FIRE number would be $1 million. Once you've saved this much, you just stick to your current monthly budget, adjusted for inflation, every year of your retirement.

It sounds like a great plan, but it doesn't take into account unplanned expenses, like a car repair, a trip to the emergency room, or replacing a broken furnace. A single large, unplanned expense can completely derail your budget, putting you at risk of running out of money prematurely.

There are a few ways around this. First, you can plan to trim your budget back in subsequent years to make up for the money spent on the emergency, but this might be difficult if you've already pared your budget down to the essentials. Or you can build a cushion into your FIRE number to include money for unplanned emergencies. 

A typical emergency fund should contain three to six months' worth of living expenses, but FIRE movement participants will want a lot more than this. It's ultimately up to you to decide how secure you want to be, but it's not a bad idea to have an emergency fund with enough money to cover a few years' worth of expenses, especially if you think your retirement could last 40 years or more.

2. Will I cost myself Social Security?

Social Security can help you supplement your savings when you're older, but you won't qualify for it if you haven't worked for at least 10 years. And you're probably short-changing yourself if you've worked less than 35 years. The Social Security Administration bases your benefit on your earnings during your 35 highest-earning years, but if you haven't worked that long, you have zero-income years weighing down your benefit calculation. Here's a guide that explains this in more detail.

If you want to leave the door open for Social Security benefits in the future, make sure you work at least 10 years before retiring. You may not care about short-changing yourself on benefits, but it's something to weigh before you retire. As your personal savings dwindle, the guaranteed income Social Security can provide might seem more appealing, so it might be worth working a little longer now to ensure larger benefits in the future.

3. What will I do if I run out of money?

Running out of money is a possibility for everyone, no matter when they retire, but it's a greater risk for FIRE movement participants because their savings has to last them a much longer time. You should have a backup plan for what you'll do if you find you're draining your savings faster than anticipated. You might plan to return to the workforce full time or part time to supplement your existing savings, or you could turn one of your hobbies into a side business that you operate during your retirement.

Check in with yourself at least annually during your retirement to see if you're spending more than you anticipated. If so, you can try to cut back, but if you have to return to the workforce for a time, it's probably easier to do this while you're still relatively young compared to waiting until you're much older and completely out of money. 

Retirement planning doesn't stop once you reach retirement, especially for FIRE movement participants. Use the above questions as a jumping-off point, but go beyond that. Think about other scenarios that could derail your plans as well and do your best to come up with contingency plans so that when you retire, it can hopefully be for good.