For many people, saving for retirement is a no-brainer. But not everyone subscribes to that school of thought.

For some, retirement savings are a nice thing to have more so than a necessity. The reason? They assume they can just fall back on Social Security instead.

Now the reality is that Social Security might end up paying you a decent-sized benefit once your time in the labor force comes to an end. But will it be enough to sustain you throughout retirement? That's questionable, to say the least.

A person with a serious expression at a computer.

Image source: Getty Images.

What can you expect from Social Security?

It's a big myth that once you're eligible for Social Security, the monthly benefit you receive will replace your former paycheck in full. If you're an average wage earner, your monthly Social Security benefit will replace around 40% of your former income. And if you're a higher earner, you can expect an even smaller percentage of replacement income.

That assumes, of course, that benefits aren't cut in the future. Right now, that's a distinct possibility. Social Security's trust funds are expected to run dry in a little more than a decade. Once that happens, the program may have to universally cut payments if lawmakers don't find a way to intervene.

But let's be optimistic and assume benefits don't get cut (it's generally in lawmakers' best interest to prevent the widespread senior poverty crisis that might ensue if that were to happen). Even so, you're still only looking at having around 40% of your former paycheck -- or less -- replaced if you retire on Social Security alone. And that's probably not enough money to live on.

For context, the average senior on Social Security today collects $1,681 a month. Come 2023, that average benefit is expected to rise to $1,827 once next year's generous 8.7% cost-of-living adjustment takes effect. But even so, a monthly benefit of $1,827 translates into an annual income of just under $22,000. If that doesn't sound like a reasonable yearly income to live on, you may need to change your approach to retirement savings -- and ramp up.

Carving out money for IRA or 401(k) plan contributions isn't easy -- not when life's many expenses get in the way. But if you don't do your best to build yourself a nest egg, you may find yourself cash-strapped and unhappy in retirement if Social Security is the only income source you're able to rely on.

Small contributions toward savings can go a long way

Now the good news is that it doesn't take a ton of money on a monthly basis to build up a solid nest egg. Contributing just $300 a month to an IRA or 401(k) over 30 years will leave you with roughly $408,000 to your name, assuming you invest your savings at an average annual 8% return during that time (that's a bit below the stock market's average and a reasonable assumption for a savings window that's three decades long).

Of course, there are steps you can take to squeeze more money out of Social Security, so you may end up scoring a higher monthly benefit than what the average senior collects today. But if you want to avoid financial struggles as a retiree, building yourself a nest egg to supplement your Social Security income is really your best bet.