No matter how diligently you save and invest, Social Security will probably play a vital role in helping you reach your retirement goals. Most people don't have access to a defined-benefit pension at work that guarantees income for life. That means Social Security benefits may be your only source of retirement income that doesn't depend on the stock market or interest rates. 

If you're expecting too much from your benefits, you're setting yourself up to struggle in what are supposed to be your golden years. Here are four dangerous assumptions about Social Security that could threaten your retirement.

A senior woman buries her face in her palm out of frustration.

Image source: Getty Images.

1. You'll be able to work until you're 70

If you want to maximize your monthly retirement checks, the best thing you can do is wait until you're 70 to start benefits. Your monthly payment will go up by 8% for every year you delay retirement benefits past full retirement age, which is 67 for people born in 1960 or later.

But even if your goal is to wait until you're 70, assuming you'll be able to do so by working until you've reached septuagenarian status is risky. The truth is, a lot of people don't get to retire on their own terms. Layoffs and medical issues often drive older employees out of the workforce earlier than they expected. Between 2008 and 2014, about 52% of workers ages 55 and up left their last job voluntarily, according to research by The New School's Retirement Equity Lab. The COVID-19 pandemic has only exacerbated this trend.

The financial pain of a forced early retirement is twofold: You may have to take Social Security earlier than you wanted, and you'll also need to stretch less retirement savings out over more time. Given all the uncertainties older workers face, it's imperative to save as aggressively as possible in your retirement accounts, regardless of how much Social Security you're anticipating.

2. COLAs will keep pace with your actual costs

Social Security recipients are getting a 1.3% raise starting in January 2021, which will add $20 to the average retiree's check. The latest cost-of-living adjustment, announced Oct. 13, should serve as your annual reminder: Social Security COLAs are ridiculously out of touch with the actual costs seniors face. Without a major overhaul of how COLAs are calculated, you can be certain your living costs will rise much faster than your benefit.

The big flaw with COLAs is that they're based on changes in the Consumer Price Index for Urban Wage Earners and Clerical Workers, or CPI-W, which excludes households that don't have at least one member in the workforce. That means retiree-headed households are left out.

An average senior spends a far greater percentage of their income on healthcare costs than a typical working-age person. Healthcare costs rise at a much faster rate than overall inflation, making it increasingly difficult for older Americans to keep up. Social Security benefits have lost approximately 30% of their purchasing power since 2000, according to a study by the Senior Citizens League, and medical expenses are the No. 1 cause.

3. Your FRA will be 67

Given Social Security's long-term solvency problems, we should expect major changes ahead. The two main ways to address the funding shortfall: Tax workers more and/or require recipients to wait longer for their benefits.

Congress last changed the FRA in 1983, so don't be surprised if this number is adjusted upward at some point. FRA is currently 67 for anyone born in 1960 or later. A report by the Congressional Budget Office suggests gradually increasing the FRA by two months for each birth year until it reaches age 70. This would reduce Social Security benefits for everyone. You could claim at the same age you planned on and get a lower benefit, or wait until your FRA and get fewer payments over your lifetime.

4. Social Security will cover most of your costs

Social Security was only intended to cover 40% of the average worker's pre-retirement income. But about a quarter of seniors rely on their checks for at least 90% of their income.

Whatever your Social Security claiming strategy, over-estimating how far your benefits will stretch in retirement is a huge mistake. It's essential that you save for your retirement so Social Security won't be your only stream of income. The average monthly benefit in 2020 is $1,523, which works out to $18,276 per year. If you'd have trouble making ends meet on an $18,276 salary, don't expect living off Social Security to be any easier.