With the average Social Security benefit providing around $18,000 of annual income, it's clear retirees can't comfortably live on that alone. Those benefits are supposed to be just one leg of a three-legged stool designed to support you in retirement, with pension and savings making up the other two legs.

Unfortunately, pensions aren't common anymore and most Americans are falling far short of the savings they need. In fact, a recent TD Ameritrade survey found nearly two-thirds of those ages 40 to 49 have less than $100,000 set aside for their later years. Even worse, just over four in 10 people in their 40s actually had less than $50,000. 

These are frightening statistics because they suggest many workers in this age group are unlikely to be able to catch up and save enough for a secure future. 

Woman looking at financial papers with calculator

Image source: Getty Images.

How much income would $100,000 provide in retirement?

If you have just $100,000 saved for retirement, this would provide you with about $4,000 in annual income if you followed the 4% rule. This rule says that you can withdraw 4% in your first year of retirement and increase the amount each year to account for inflation. It is intended to help you pick a safe withdrawal rate so you don't take too much money out of your accounts too soon. 

If you withdraw a larger amount (say, around $10,000 per year), your money would be gone in about 13 years. And that's assuming you didn't increase your withdrawal rate from year to year and earned around a 6% return on your investment. Most people will live longer than 13 years in retirement and will need their savings to produce more than $10,000 -- and definitely more than $4,000 a year. 

Can you save enough for a secure retirement if you have less than $100,000?

The specific amount you'll need for retirement varies depending on your situation, including your cost of living and how much you get from Social Security and other sources. 

For many people in their 40s, saving about $1 million is a reasonable goal for retirement. This would give you an income of $40,000 if you follow the 4% rule. When combined with Social Security, that should provide a reasonable sum even after accounting for the impact of inflation on your buying power. 

If you have $100,000 saved already and start at 40, you could hit $1 million by 65 provided you save about $528 a month and earn a 7% annual return on investment. 

But unfortunately, the TD report shows that nearly two-thirds of those in their 40s have less than $100,000 -- so they're starting from further behind. And 41% of people in this age group have under $50,000. If you're starting with just $50,000, you'd need to raise your savings to $881 per month. And if you have nothing at all saved, you'd have to put aside $1,235 monthly!

While it may be possible to hit the $1 million goal if you start right at 40 and get aggressive about saving, for many people, saving this much will simply be out of reach. 

What to do if you're in your 40s with less than $100,000 saved

If you're one of the millions of Americans in your 40s with a small retirement savings balance, you'll need to make some big budget cuts today to start aggressively saving for your later years. You may even want to pick up an extra job to earn more to save.

While having too little saved by your 40s isn't ideal, you still have time to change course. But the sooner you act, the easier it will be to turn things around and become a financially secure senior.