Working Americans are often urged to save independently for retirement, rather than rely on Social Security alone to pay the bills when they're older. But a troubling number of U.S. adults aren't making decent headway in this regard.

An astounding 42% of Americans have less than $10,000 socked away for retirement, and while that figure includes younger workers with a chance to catch up, it also encompasses near-retirees on the cusp of leaving the workforce. And it's the latter group that's really in trouble, because banking on Social Security by itself in retirement means signing up to be cash-strapped for decades.

Older man holding his head while sporting a serious expression

IMAGE SOURCE: GETTY IMAGES.

Social Security alone won't cut it

Though Social Security can serve as a nice supplement to existing retirement savings, it's not equipped to sustain seniors by itself. The average beneficiary today collects $1,479 a month in benefits, or $17,748 a year. If you're an average earner planning to retire in the near future with no savings, and no pension or other viable source of income, then you can expect a similar annual income once your career closes out.

But chances are, $17,748 a year won't suffice in paying your bills. And if you think it will, ask yourself: "Am I spending much more than $17,748 a year now?" Because if you are, then you'll need to reassess your retirement plan -- and start ramping up on the savings front immediately.

Boost your nest egg while you can

If you're within a few years of retirement, you unfortunately don't have a huge window of time to make up for decades of not saving. But that doesn't mean all is lost.

First, write up a budget so you can distinguish between your essential expenses, and those that can be cut. Then, do some cutting. Cancel cable, avoid dining out at restaurants, get rid of a car you can technically get by without, or do whatever you can to scrape together some cash.

Next, look at getting a second job. It may not be your ideal move given the career stage you're at, but it's a guaranteed way to drum up extra money.

Finally, aim to work longer than planned. Maybe that means extending your career by a year, or two, or three or more. The key is to give yourself as much opportunity to save as possible.

Now, let's imagine that the above moves allow you to sock away $1,500 a month over a six-year period. If you invest that money at a conservative average annual return of 4%, you'll end up with close to $120,000 in retirement savings. Frankly, that's still not a ton of money -- but it's better than nothing.

If you're without a nest egg but aren't as close to retirement, your prospects are even brighter. If you're able to save $1,500 a month over a 12-year period, and invest that money at a more aggressive average annual 7% return (that's feasible with a stock-heavy portfolio, and you can feel more comfortable loading up on stocks with a 12-year investment window), you'll end up with about $322,000. That's more comforting.

No matter how much money you're able to scrounge up for your golden years, know this: You really can't live comfortably on Social Security alone. So if you don't go into retirement with an additional income source, you're going to have to make major sacrifices. That could mean downsizing to a smaller home, or relocating to a less ideal part of the country because it's cheaper. Granted, these options are on the table if things come to that. But be prepared to embrace them, if you're looking at sustaining yourself on $17,748 a year and nothing more.