Your senior income will need to come from somewhere, and unless you're privy to a pension, which many workers today are not, you'll most likely rely on a combination of Social Security benefits and retirement savings to cover your bills once your time in the workforce wraps up. Social Security will probably replace around 40% of your pre-retirement income, provided you're an average earner. But most seniors need roughly double that amount to live comfortably, and so if you want to enjoy your golden years, you'll need a healthy level of savings in your IRA or 401(k).

But a large number of older Americans are behind in this regard, reports TD Ameritrade in a new survey. An estimated 37% of workers in their 50s, 28% of workers in their 60s, and 20% of workers in their 70s have less than $50,000 socked away for the future. And these are the people who really need to catch up.

Fanned-out stack of 100-dollar bills against a blue background

IMAGE SOURCE: GETTY IMAGES.

Thankfully, that option is very much on the table with IRAs and 401(k)s, as both plans allow workers 50 and over to contribute more money on an annual basis than their younger counterparts. Younger workers can contribute up to $6,000 a year to an IRA, but for those 50 and over, that limit increases to $7,000. Meanwhile, workers under 50 can put up to $19,500 into a 401(k), but that limit rises to $26,000 among those 50 and older.

But despite the option to make catch-up contributions in an IRA or 401(k), 69% of workers aged 50 to 79 aren't taking advantage of it. If you're behind on building savings, you'd be wise to capitalize on the catch-up option in your retirement plan. Otherwise, you may not be happy with your financial picture later on.

What can catch-up contributions do for you?

As a general rule, it's a good idea to aim to close out your career with 10 times your ending salary saved up. If you're not all that far away from retirement and are also nowhere close, then taking advantage of catch-up contributions could be your best bet.

Imagine you're 55 with $40,000 in your IRA and that you're aiming to retire at age 70. If you contribute $6,000 a year to that plan over the next 15 years, and your investments generate an average annual 7% return (which is doable when you invest heavily in stocks), you'll grow your balance to about $261,000. But if you max out your IRA at $7,000 a year instead during that decade and a half, you'll wind up with a little more than $286,000. And that extra $25,000 could make a huge difference down the line.

The gap between making catch-up contributions or not gets even wider with a 401(k). Let's adjust the above scenario to account for 401(k) limits. If you're starting with $40,000 at age 55 and contribute $19,500 to your savings over 15 years, you'll wind up with about $600,000, assuming an average annual 7% return. But if you take advantage of catch-ups in that account, socking away $26,000 annually for the next 15 years instead, you'll end up with close to $764,000.

Of course, if you're doing fairly well savings-wise and are on track to retire with 10 times your ending salary or more, then you may not need to push yourself to make catch-up contributions to your IRA or 401(k). But if you're behind on savings, don't miss out on that key opportunity to make up for lost time.