Despite growing recognition of the benefits of delaying when to start taking Social Security, a new survey by Fidelity Investments found that nearly half (45%) of 61-year-old Americans expect to tap into Social Security at age 62, their first year of eligibility.

Among those planning to do so, 77% said they will use Social Security to pay for basic needs such as food and utility bills. This group expects their Social Security payments to comprise nearly half (49%) of their total retirement income, but only 22% know exactly how much their check will be. And 73% of those planning to start taking Social Security at age 62 don't have a formal retirement income plan.

What's more, many people in this group don't know all of the ins and outs of Social Security benefits. While 85% of them correctly identify age 62 as the earliest they can collect Social Security checks, only 56% know when they will be eligible for full Social Security benefits (age 66, for those born 1943-54). And only 54% know they need to file for their benefit three months in advance of the date they wish to start receiving payments.

More important, 31% believe Social Security payments aren't taxable and 12% aren't aware that working in retirement could impact their benefits.

"Many Americans who are within one year of beginning to collect their Social Security retirement benefits may be planning to rely too much on it, considering Social Security currently only funds a little more than one-third, or 37%, of an average retiree's income," said Carolyn Clancy, executive vice president at Fidelity Investments Personal and Workplace Investing, which provides resources on the impact of Social Security on retirement planning.

That's why some observers believe it pays to delay taking Social Security benefits for those who don't urgently need the money. "A lot of people underestimate how big an impact delaying retirement and Social Security can have," says Stuart Ritter, a certified financial planner at T. Rowe Price.

The first wave of baby boomers turn 62 this year. According to T. Rowe Price research, a person who is currently 62 years old and delays retirement until age 65 and makes $100,000 each year until benefits begin will boost their eligible Social Security benefits by 27%, (in today's dollars) based on Social Security Administration formulas. Waiting until age 70 to retire will bolster benefits by 88%.

In their book "Working Longer: The Solution to the Retirement Income Challenge," authors Alicia Munnell and Steven Sass state that people who worked full-time until at least age 66 could boost their income one-third higher than if they retired at 62.

But they also acknowledge that working longer isn't feasible for everyone, and that up to one-third of older workers could find it difficult to work into their mid-60s due to poor health or job prospects.

Fidelity's survey of 600 Americans ages 55 to 69 was conducted in August.