(cnbc.com) And you thought feathering your nest egg was tough. As you transition from collecting a paycheck to living off your savings, which for most occurs in their 60s and early 70s, all those years of retirement planning get put to the test.

You'll need to determine how much you can safely withdraw from your portfolio so you don't deplete your principal, convert your collection of taxable and tax-deferred accounts into a stable income stream and adjust your asset mix to minimize market shocks.

"The transition from accumulation to deaccumulation poses a psychological as well a financial challenge," said Bob Adams, a certified financial planner with Armstrong Retirement Planning. "It requires financial planning, as well as some key choices and trade-offs for the retirees around their own goals and objectives."

Longevity risk, or the chance you'll outlive your money, is by far the biggest threat to a secure retirement. The best defense on that front is a good offense, he explained.

Before you call it quits on your career, Adams advises crunching the numbers to ensure your savings are sufficient to maintain your standard of living.

Evaluate your assets and project your retirement income, including pensions and Social Security, along with your living expenses—for example, mortgage, car payments and travel—to determine whether you can comfortably cover your bills.

"Too many blindly and arbitrarily retire at a certain age without regard to the financial ramifications," Adams said. "Many retirees find that the costs of medical care and protecting against longevity are much higher than they may have expected."

Delaying retirement by even a year or two, he noted, can improve your future cash flow significantly.

Not only does extra time in the workforce allow you to continue contributing to your individual retirement account (IRA) or 401(k) plan, but it also gives your nest egg the chance to deliver compounded returns longer.

Read more here: How to avoid outliving your retirement nest egg