Susan Kelechi Watson as Beth and Sterling K. Brown as Randall on NBC's "This Is Us"

By the time you're in your 40s, you're entering your peak earning years and could be more than halfway to retirement. How prepared are Gen Xers for their golden years? CNBC Make It turned to Fidelity, the nation's largest retirement-plan provider, for the numbers. As of the first quarter of 2019, Americans between 40 and 49 years old had an average 401(k) balance of $102,700 and were contributing 8.5% of their paychecks. Fidelity also found that employers were matching, on average, 4.9%, which put the total savings rate for 40-somethings at 13.4%.

Here are the average contribution rates by age, also from Fidelity. These rates do not include any matching contributions from employers.

Keep in mind that Fidelity's data only takes into account those Americans with a retirement account so it doesn't present the full picture. Almost a quarter of U.S. adults have no retirement savings and just 36% of non-retired adults believe their retirement saving is on track.

How much should I be saving for retirement?

The answer to this is highly personal and depends on your lifestyle, expenses and spending habits, but there are a few basic guidelines to follow if you want to retire comfortably. Fidelity recommends saving 15% of your salary toward retirement, and that amount includes contributions from your paycheck as well as any contributions from your company. The goal is have 10 times your final salary in savings by retirement. If you want to retire at 67, Fidelity has a timeline to use in order to hit that magic number: By age 40, it recommends having three times your salary saved; by age 45, four times; and by age 50, six times. Ultimately, though, everyone's scenario is different. If you're getting a later start on saving, you will have to save more to catch up. In a 2018 report, the Stanford Center on Longevity determined that if you want to retire by age 65, you should be setting aside 10-17% of your income if you start saving as early as age 25. But if you wait until 35 to start, you have to save 15-20%. To help you figure out the right amount to fund your retirement, try using a retirement calculator.

How do I get on track?

If you're not setting aside 10-15% of your income for retirement, or you don't have the equivalent of three times your salary saved by age 40, don't panic. There are strategies you can use that will help you get to, or nearer to, where you need to be. First things first, enroll in your employer-sponsored 401(k) plan if you haven't already, says Katie Taylor, vice president of thought leadership at Fidelity Investments. Next, find out if your company offers a 401(k) match. If they do, take full advantage of it, she tells CNBC Make It: "If there is a match that's 3%, make sure that you're saving at least 3%. Otherwise, you're leaving free money on the table." Most importantly, start setting aside money now. "It's harder to catch up if you don't save," says Taylor. "If you spend the first half of your career not saving, you've got to do a lot of catching up later in your career and you don't have the time in the market to ride out any fluctuations. It's always a good idea to get started as early as possible."

What if I don't have a 401(k)?