Do you have any idea what the average monthly Social Security retirement benefit is? It was recently $1,375, which amounts to just $16,500 per year. Clearly, you're probably not going to live comfortably in retirement solely on Social Security income.

It's important to know what to expect from retirement, so that you can best plan and prepare for it. Here are 15 rather important or impressive things to know.

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56%

More than half of workers are planning to keep working part-time in retirement, at least for a while. That's a reasonable goal, given how underprepared most people are, financially, for retirement.

44%

Only 44% of single people are saving for retirement, compared with 63% for married folks, according to a TD Ameritrade survey. The disparity makes sense because two-income households can find it easier to save, but both percentages are lower than they should be.

24%

According to the 2016 Retirement Confidence Survey, about a quarter of workers surveyed -- as opposed to retirees -- said they had less than $1,000 saved for retirement, not including pension or home values. About two-thirds of them had saved less than $100,000. The following table shows more detail:

Amount Saved for Retirement*

Percentage of Respondents

Less than $1,000

24%

$1,000 to $9,999

14%

$10,000 to $24,999

9%

$25,000 to $49,999

8%

$50,000 to $99,999

10%

$100,000 to $249,999

15%

$250,000 or more

20%

Data source: 2017 Retirement Confidence Survey. 

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$10,000

Even if you have $250,000 socked away for retirement, it's not likely to be enough. If you use the flawed-but-still-useful "4% rule" for drawing down your nest egg in retirement, a $250,000 nest egg will give you just $10,000 of income in your first year.

80%

So how much retirement income do you need? Well, there's no one-size-fits-all number, but some experts suggest aiming for 80% of your income at the time you retire. So if you retire earning $75,000, you'll want to aim for $60,000.

25

One way to get a rough idea of how much you need to save is to invert the 4% rule and multiply your desired annual income from your nest egg by 25. So, for example, if you want to be able to draw $20,000 from your nest egg in your first year of retirement, you'd multiply that by 25, getting $500,000. You'd need to retire with $500,000 saved.

67

Here's an interesting retirement detail: Many people assume that retirement generally starts at age 65. But only 26% of workers know what their "full" retirement age is -- the age at which they can start collecting Social Security. It's actually 67 for many of us:

Birth Year

Full Retirement Age

1943 to 1954

66

1955

66 and 2 months

1956

66 and 4 months

1957

66 and 6 months

1958

66 and 8 months

1959

66 and 10 months

1960 or later

67

Data source: Social Security Administration.  

63

Regardless of full retirement ages, the average retirement age was recently 63. 

62

The earliest age at which you can start collecting Social Security retirement benefits is 62 -- and it's also the most common age at which people do start collecting. That means they get smaller checks, though -- but they'll get many more of them.

70

The longer you delay starting to collect Social Security, up to age 70, the bigger your ultimate checks will be. They increase by about 8% for every year beyond your full retirement age that you delay.

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46%

Don't assume that you can retire at 70 or any particular age, because many people end up retiring earlier than planned. Fully 46% of retirees left the workforce earlier than planned, with 55% citing health problems or a disability as the reason and 24% citing changes at work such as a downsizing or workplace closure, according to the 2016 Retirement Confidence Survey.

$275,000

Be sure to factor healthcare costs into your retirement plans. A 65-year-old couple retiring today will spend, on average, a total of $275,000 out of pocket on healthcare, according to Fidelity Investments.

10%

Speaking of healthcare, don't be late enrolling for Medicare, because it can cost you. Your Part B premiums -- which cover medical services, but not hospital services -- can rise by 10% for each year that you were eligible for Medicare but didn't enroll. The no-penalty enrollment period for most people is anytime within the three months leading up to your 65th birthday, during the month of your birthday, or within the three months that follow.

90%

Most elderly beneficiaries get 50% or more of their income from Social Security, while 23% of married ones and 43% of unmarried ones get fully 90% or more of their income from it, according to the Social Security Administration.

90 years

Here's a last stat that should drive home the importance of planning and saving for retirement: 30% of 50-year-old women and 19% of 50-year-old men will live to 90, according to the Social Security Administration. So even if you retire as late as 70, you stand a decent chance of needing to live off your savings for 20 more years.

The better prepared you are, and the more you have socked away for retirement, the better your retirement is likely to be.

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