As more and more American workers reflect on their ability to secure a financially comfortable retirement, the mismatch between when they think they will retire and when they actually do provokes both concern and reflection. Retirement ages have undoubtedly increased over the past decade — a 2015 analysis by the Centre for Retirement Research at Boston College points to an increase of one year for men (from age 62.9 to 63.9) and approximately half a year for women (from age 61.2 to 61.9). However, not everyone is able to control retirement timing.

A 2014 Employee Benefit Research Institute (EBRI) study found that 49 percent of retirees surveyed had retired earlier than they had planned. This finding is consistent with a recent report from Merrill Lynch/Age Wave in which more than half — three out of five — retirees say they retired earlier than they had expected.

Disconcertingly, lack of financial preparedness is one of the key drivers behind the desire to work longer and delay retirement. The Survey of Household Economics and Decision-making (SHED) captures this financial fragility — a lack of retirement savings and minimal financial cushion. Similarly, 31 percent of workers surveyed in the EBRI study say they have no retirement savings or pension.

Across industries, the projected shortfall for the average worker was found to be 2.2 times that of pay — specifically ranging from 1.1 times pay in the energy industry to 5.8 times pay in the retail industry. In 2014, average 401(k) balances at Fidelity were $91,300, whereas a 65-year-old couple retiring that year could be expected to spend an average of $220,000 during retirement on out-of-pocket health care costs alone.

Improved longevity also mandates the need to have more savings. Life expectancy projections by the Society of Actuaries show that compared to 2005, people retiring at age 65 in 2014 should plan for an additional three years of retirement on average.

Also, studies show that workers covered by 401(k) plans retire a year or two later on average. Clearly, the imperatives of personal responsibility on account of the shift from defined benefits to defined contribution pension plans contribute to the desire to push retirement further.

But financial distress is not the sole motive behind the desire to work longer. Psychological and social fulfilment — a desire for continued productivity, stimulation, satisfaction and social connections — are important drivers as well behind the aspiration to continue to work in later years. Indeed, the oldest age segments of the workforce are often more likely to be engaged than younger workers. Aon Hewitt data show that 65 percent of employees ages 55 and older in large companies are engaged, compared to less than 60 percent of employees under age 45. This is significant as a 5 percent increase in engagement levels has been shown to increase revenue within organizations by 3 percent.

It is also likely that a multi-generational workforce creates a fertile ground for knowledge transfer and mentoring, where the younger workers stand to gain from the “maturity, real-world knowledge and business skills of older workers.”

However, all the virtues of older workers and their attendant benefits to employers and society notwithstanding, the need to meticulously plan in advance for retirement remains paramount. “People consistently overestimate their ability to work in retirement,” says Vandermillen, vice president at Principal Financial Group. The somewhat naïve intent to continue to work longer to address the financial imperatives is “likely to be a failed strategy for many.”

A host of factors such as health crises, layoffs and ageism on the part of prospective employers can force people out of work earlier than they had planned. "The difference is between what you know you want to do and what factors outside your control ultimately require you to do," says Dallas Salisbury, president of EBRI.

John Hoffmire is director of the Impact Bond Fund at Saïd Business School at Oxford University and directs the Center on Business and Poverty at the Wisconsin School of Business at UW-Madison. He runs Progress Through Business, a nonprofit group promoting economic development. Pankaj Upadhyay, Hoffmire’s colleague at Progress Through Business, did the research for this article.