Once you retire, it's fair to assume that you're going to need to replace a pretty large chunk of your former income.

It's true that some of your expenses may decline in retirement. But you'll still need to pay for shelter (at least to some degree), transportation, food, utilities, and healthcare. And these costs can easily add up, which is why it's important to try to retire with a nice amount of savings.

A Social Security card.

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But what if you're approaching your senior years without a particularly large IRA or 401(k)? It may be that you struggled to save because you didn't earn the highest wages, or you had to take time off at several points during your career to be a caregiver.

Delaying your Social Security claim is a good way to make up for a lack of savings -- at least in theory. But it's also not a plan you should bank on.

The upside of delaying Social Security

You're entitled to your complete monthly Social Security benefit based on your personal wage history once you reach full retirement age. That age is 67 for anyone born in 1960 or later.

If you delay your Social Security claim past full retirement age, your monthly benefits increase by 8% for each year you do. And while this incentive does run out at age 70, you have an opportunity to boost your monthly Social Security checks by 24% (or more, if you were born before 1960 and have an earlier full retirement age) for life.

It's a pretty good deal when you think about it. All you have to do is keep working past full retirement age so you can wait to file, and those larger monthly checks are a sure thing. But working longer may not be something you're able to do.

There's no guarantee that you'll be able to delay

It's certainly possible that you'll have the option to delay Social Security once you reach full retirement age. But if you don't have much savings, the only way to really pull that off is to continue working. And there's no guarantee you'll be able to hold down a job at that point in life.

For one thing, you may be forced to retire due to health issues, whether they're your own or a loved one's. Also, while it's certainly illegal to force people into retirement once they reach a certain age, it's also a hard thing to prove. For this reason, companies manage to get away with laying off older workers all the time without legal repercussions.

Put another way, if your employer decides they want you gone at 67, hanging onto your job may be very difficult -- even if you're great at it. And if you can't work beyond 67, then it's hard to keep delaying your Social Security claim.

Have a different plan

There's nothing wrong with hoping to claim Social Security at 70, or at some point beyond full retirement age. But it's not something you should bank on being able to do. And you certainly shouldn't count on a delayed filing to make up for a lack of savings.

If you're getting closer to the end of your career and you aren't happy with your IRA or 401(k) plan balance, make changes. Cut back on spending for a few years to squeeze more money into your retirement account. And if needed, get yourself a side gig temporarily if the opportunity is there.

It can certainly be worth holding off on Social Security for the promise of larger monthly benefits. But you also can't assume that you'll be able to delay your claim. And you need a backup plan in case that isn't able to happen.