By the time you reach age 55, you likely have 15 years or less to go before you retire. That's why it's so troubling that the Federal Reserve's 2016 Survey of Consumer Finances found that workers between the ages of 55 and 64 had an average retirement savings balance of just $135,000, which is not nearly enough to provide the income retirees need to live in comfort and financial security.

If you're 55 or older and your retirement savings are around that amount, or even lower, then you need to take action -- fast.

Why that's not enough money

While $135,000 may sound like a lot of money, your retirement savings will need to be your primary source of income for decades. To avoid exhausting your savings, you must limit yourself to withdrawing a small percentage of your balance each year.

Let's say you follow the 4% rule, withdrawing 4% of your savings in your first year of retirement and adjusting that amount for inflation each year afterward. A retirement account containing $135,000 would provide you with an income of $5,400 in the first year, or $450 per month. That's an awfully small income to live on, even with Social Security benefits to help.

To make matters worse, that's an optimistic scenario: While the 4% rule was once accepted as the best guideline for planning your retirement distributions, it has recently come under fire as potentially being too aggressive. That means you may be limited to no more than 3% to 3.5% of your retirement savings for income each year, at least during your first few years of retirement.

Money in envelope labeled 401k

Image source: Getty Images.

How much retirement savings do you need?

There are countless retirement calculators floating around the internet that can help you pin down a retirement savings goal. The problem is that they produce widely varying results, making it tough to figure out which one has the "right" answer.

The amount you'll need to save up depends on how high your retirement expenses will be. Your savings will need to provide enough income to cover all your expenses, as well as potential emergencies and the occasional splurge. To accurately estimate your retirement expenses, you'll need to not only add up all your expected bills, but also account for how you plan to spend your time. After all, you'll have a lot of time on your hands, so how you choose to spend it will have a major impact on your finances. As a soon-to-be senior citizen, you'll also need to plan for expenses like rising medical bills and long-term care services.

When calculating retirement expenses, you can use your current expenses as a guideline and then make any necessary adjustments. For example, you may find that you can cut your transportation costs in half, since you won't be commuting to work -- but you may also need to double your travel budget. It's a good idea to build at least a 10% margin of error into your expense calculations for emergencies and other unexpected expenses. For example, if you do the math and decide that your retirement expenses will be $3,000 per month, aim for a retirement income of at least $3,300 per month to allow room for error.

What if you don't have enough?

If you're among the millions of Americans approaching retirement age who don't have enough saved, today is a good day to start turning things around. The easiest way to shift your retirement budget into the black is to delay retirement by a few years. Every year that you keep on working is another year when you'll be adding to your retirement accounts instead of taking money from them.

You'll also need to kick your retirement contributions into high gear. Ideally, you'll max out your annual contributions for whichever type of retirement account you have (IRA, 401(k), or even both). Once you hit age 50 you'll be able to make catch-up contributions that push those annual limits up a bit. Being able to save large amounts of money late in the game may be enough to turn your financial situation around.

For example, a 55-year old saver can put up to $24,000 per year into a 401(k). Doing so for 10 years will increase their retirement savings by $354,806, assuming an average 7% rate of return. Of course, that would also require making sacrifices today, like drastically cutting expenses, supplementing income by taking on a part-time job, or both. The good news is that these sacrifices are strictly short-term measures, as you're relatively close to retirement anyway.

Finally, make sure an ample percentage of your portfolio is in stocks, rather than bonds. You can use the retirement allocation formula of 110 minus your age to figure out what percentage of your portfolio should be in stocks, while the remainder can go in bonds. For example, if you're 55, this formula would tell you to put 55% of your money in stocks and the remaining 45% in bonds. When you're behind on retirement savings, you'll want to have at least as much in stocks as the formula recommends; you can even increase your stock allocation by an additional 10% if you can tolerate the increased risk.

Stocks produce much higher average annual returns than bonds do (around 10% for large-cap stocks over the long term, versus 5% for bonds), but they come with a higher risk of crashing in value just when you need to start using that money. Still, if you don't have any other way of boosting your retirement savings, it may be worth taking on a bit of extra risk to build up some extra savings before you retire. Extra returns likely won't solve all your money problems, but they will certainly help.