A big reason so many seniors wind up miserable is that they don't save adequately for retirement ahead of time. And why don't they save? For some people, it's a matter of low earnings and a true inability to squeeze out IRA or 401(k) contributions. For others, however, it's a matter of underestimating the cost of retirement and not realizing the importance of having multiple income streams during that time. Here are a few good reasons why you really, really need to save for your senior years -- even if you're convinced otherwise.

1. Social Security won't pay you all that much

Many people assume that once they retire, they'll be able to get by on Social Security. But in reality, the average beneficiary today only gets about $1,500 a month. Now even if you're convinced you'll spend a lot less in retirement, do you really think $18,000 a year is going to cut it? Furthermore, if you have any desire to enjoy life during retirement -- say, to travel and pursue hobbies that may not be free -- then you're going to need way more than Social Security income to support that lifestyle. Hence, the need for savings.

Smiling older man and woman at laptop

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2. Social Security may get cut

That $18,000 a year in Social Security income we just talked about? It may not even happen. Benefit cuts are on the table as the program grapples with a massive income shortfall, and so the $1,500 monthly sum you'd normally be entitled to could instead shrink if lawmakers don't intervene with a fix. Having savings, however, can compensate.

3. Your healthcare costs are likely to climb

Seniors tend to have more health problems than younger people, so it may not surprise you to read that your medical costs are likely to rise during retirement. But you may be shocked to learn that some projections are now calling for a total healthcare spending tab of $606,337 throughout retirement for the typical 65-year-old couple today. Now, let's be optimistic and say that Social Security isn't cut. Even so, do you really think your $18,000 a year in benefits will be enough to cover your living expenses plus medical care? Probably not, so you'll need savings to bridge that gap.

Growing your retirement savings

By now, you should be convinced that you'll need savings to manage financially once your career comes to a close. The question is: How much money should you part with?

The answer depends largely on your goals. If you expect to live frugally as a senior, saving $300 a month might cut it. If you want to live it up during retirement and travel the globe, you may need to save a lot more.

The amount of time you have to save money will matter, too. The longer you have to build retirement wealth, the less money you may feel compelled to part with on a monthly basis. Check out the following graph, which shows how much of a savings balance you stand to accumulate if you sock away different monthly sums over a 35-year period.

Graph showing retirement plan balances

Image source: Author.

Of course, an additional factor that will come into play is the way you invest your savings. The figures above assume a 7% average annual return, which is reasonable if you load up on stocks in your retirement plan. Play it safer, and your results will be different.

Either way, do yourself a favor and don't buy into the myth that you'll manage to get by in retirement without a solid IRA or 401(k). If you don't make an effort to save, you're likely to wind up very, very sorry down the line.