The vast majority of Americans, 78 percent, say they're "extremely" or "somewhat" concerned about not having enough money for retirement, according to Northwestern Mutual's 2018 Planning & Progress Study.

And for good reason: A shocking 21 percent of Americans have nothing at all saved for the future, and another 10 percent have less than $5,000 tucked away, the study finds.

That means about a third of Americans have only a few thousand dollars, or less, put away for their golden years.

Of course, some people are more prepared: A quarter report having $200,000 or more stashed away, while 16 percent have between $75,000 and $199,999. But overall, Northwestern Mutual found that Americans with retirement savings have an average of $84,821 saved, which is far from enough. Experts typically recommend trying to accumulate at least $1 million.

Meanwhile, a new survey from Bankrate finds that 13 percent of Americans are saving less for retirement than they were last year and offers insight into why much of the population is lagging behind. The most popular response survey participants gave for why they didn't put more away in the past year was a drop, or no change, in income.

"That's consistent with federal data that show real wages have barely budged in decades," Bankrate reports. According to the Pew Research Center, the average paycheck has the same purchasing power it did 40 years ago.

Day-to-day costs continue to soar, and salaries don't go as far as they once did to cover the necessities, author and executive director of the Economic Hardship Reporting Project Alissa Quart tells CNBC Make It. That makes it more difficult to set aside money for the future.

Still, the longer you put off planning for your golden years, the farther behind you'll fall.

The good news is there are ways to make progress without feeling cash-strapped or committing to any drastic lifestyle changes. Here are three effective strategies:

1. Start ASAP. The sooner you begin putting your money to work, the less you'll have to save each month to reach your goals, thanks to the power of compound interest.

If you start at age 23, for instance, you only have to save about $14 a day to be a millionaire by age 67. That's assuming a 6 percent average annual investment return. If you start at age 35, on the other hand, you'd have to set aside $30 a day to reach seven-figure status by age 67.