Millions of seniors rely on Social Security to pay their living expenses in retirement. But one thing you need to realize about those benefits is that they're not set in stone. A calculation based on your earnings history will give you the full monthly benefit amount you're entitled to upon reaching full retirement age, which, depending on your year of birth, is either 66, 67, or somewhere in between at 66 and a certain number of months. But you actually get an eight-year window to file for Social Security that spans the ages of 62 to 70, and the age at which you initially take benefits has an impact on your payments.

Now as you might expect, filing for benefits ahead of full retirement age will result in a reduction, while waiting past full retirement age will allow your benefits to grow. Therefore, while you may be inclined to claim benefits at 62, doing so will result in the largest possible reduction you could face. And that's reason enough not to file right away.

Senior couple looking at a map

IMAGE SOURCE: GETTY IMAGES.

That said, there are certain scenarios where taking benefits at 62 is the right thing to do. Here are three you should know about.

1. You're unemployed

Maybe you got laid off when your company downsized. Or maybe you clashed with your manager, which eventually resulted in your termination. If you're eligible to collect Social Security, and you don't have enough savings to live on, then filing for benefits makes much more sense than using a credit card to keep up with your expenses.

Of course, there's also the possibility of holding off on benefits and aggressively looking for another job -- but you'll need strong savings to allow for that, since you might, unfortunately, struggle to find work. Boston College researchers found a couple of years back that unemployed adults aged 55 and over were less likely to get hired than younger workers despite their vast experience. And in a 2012 study by the Urban Institute, workers in their 50s were 20% less likely to find new jobs than workers 20 to 30 years their junior. In other words, if you're out of work come age 62, things might stay like that for a while, so you're better off using your Social Security benefits to compensate than wrecking your finances by racking up debt.

2. Your health is poor

One interesting facet of Social Security is that it's designed to pay you the same total lifetime benefit regardless of when you initially file. The logic is that reductions in payments for filing ahead of full retirement age are offset by the larger number of individual payments you get to collect in your lifetime. This formula, however, assumes that you live an average lifespan, so if your health is in bad shape and you don't think you'll live as long as your peers, filing early will generally give you the most money from Social Security in total.

Imagine you're entitled to a full monthly benefit of $1,500 at a full retirement age of 67. Filing at 62 will reduce each payment to $1,050, but you'll collect 60 more payments. If you end up living until 78-1/2, you'll wind up with more or less the same total in Social Security income regardless of whether you file at 67 versus 62. But what if you only live until 73? In that case, you'd come out over $30,000 ahead by filing at 62 rather than waiting.

It's never pleasant to contemplate one's mortality, but you do need to be honest about the state of your health and factor it into your decision of when to claim Social Security. And if you come to realize you probably won't have all that long a retirement, then filing at 62 is the way to go.

3. You have a spouse whose benefits can continue to grow

Married couples where both parties are entitled to Social Security have an advantage in that they can work together to maximize those benefits. Now let's say you and your spouse want to retire at 62, but you don't have quite enough savings to make that happen. If that's the case, it could make sense for one of you (typically the lower earner) to file for benefits at 62, while the other leaves his or her benefits alone to continue growing. This way, you get the best of both worlds: access to the money you want or need right away, all the while ensuring that your second set of benefits isn't reduced.

Though there are plenty of good reasons not to file for Social Security at 62, if the above circumstances apply to you, claiming as early as possible can actually be a smart idea. Either way, assess your options carefully before making your move, because this is one retirement decision you really want to get right.

The Motley Fool has a disclosure policy.