Many seniors get the bulk of their income from Social Security, and you may be planning to do the same once it's your turn to retire. But while you might think that's a reasonable idea, these three facts will point you in the opposite direction.

1. The average monthly benefit is just $1,543

The average senior on Social Security today collects $1,543 a month, or $18,516 per year, in benefits. And chances are, that won't be enough money to cover your bills.

Even if your home is fully paid off by the time you enter retirement, you'll need to maintain that home and cover insurance and property taxes. Plus, you'll still need to put food on the table, pay utilities, and insure and maintain a car to get around town (unless you happen to live in a city and can rely on public transportation -- but even that will cost some money).

There's also healthcare to consider. A good 40% of seniors today spend over $750 a month on medical expenses. If you retire on just Social Security, you could easily end up spending half of your income on healthcare, leaving you with very little money to cover your remaining bills.

Five Social Security cards resting on each other

Image source: Getty Images.

2. Cost-of-living adjustments have averaged just 1.65% over the past 10 years

The monthly benefit you start out collecting from Social Security won't be the same amount you receive for life. Each year, seniors are entitled to a cost-of-living adjustment, or COLA, that serves as a raise.

But COLAs have been stingy of late. Between 2012 and 2021, they averaged just 1.65%. Meanwhile, a 1.65% raise would bring today's average $1,543 benefit up to just $1,568. A 1.65% raise the next year would increase that benefit to $1,594. These incremental increases may be helpful, but as you can see, they're far from life changing.

3. Benefit cuts are on the table

Social Security is facing a serious financial shortfall that could result in benefit cuts across the board. While that's technically not set in stone, last year, the program's Trustees pointed to a 24% reduction in benefits as early as 2035. If that were to happen, today's average monthly benefit of $1,543 would shrink to $1,173, leaving current and future seniors with even less money to live on.

Lawmakers are invested in finding a way to avoid benefit cuts. Joe Biden, for example, is proposing to increase Social Security taxes for higher earners to pump more money into the program. But still, you can't discount the possibility that benefit cuts are on the way.

You need a backup plan

There's nothing wrong with factoring some income from Social Security into your retirement number crunching. But don't make the assumption that you'll be able to live on those benefits in the absence of outside income.

Instead, have a game plan. Sock away money in a dedicated retirement plan, like an IRA or 401(k). If you set aside $250 a month for 25 years, you'll end up with $190,000 if your investments in that account generate an average annual 7% return, which is a reasonable assumption for a portfolio that's loaded with stocks.

If that doesn't work -- say you're already on the cusp of leaving the workforce and don't have decades ahead of you to save -- plan to work part-time in retirement. You can even see about renting out part of your home and using that to supplement your benefits.

The choice is yours, but do something to help ensure that Social Security isn't your sole income source as a senior. Otherwise, you could wind up dangerously cash-strapped for decades.