You've got more than enough cash to cover your living expenses during retirement -- plus, perhaps, a little extra to pay for travel, entertainment and potentially higher medical expenses down the road.

Or do you?

Even the most financially flush retirees can deplete their savings in short order if they don't establish a sustainable withdrawal strategy and stick to it.

Indeed, the secret to making your nest egg last is not how much you've got, but how well you manage your cash flow.

"Withdrawal rates are the most important factor because you've got a limited supply of assets in retirement," says Tom Balcom, a certified financial planner with Foldes Financial Management in Miami. "You have to be sure you know what to expect, and be ready to adjust your withdrawal rate if the market declines."

Smart withdrawal strategies

• Withdraw 4 percent to 6 percent of fund annually. • Tap taxable accounts first, Roth IRAs last. • Have one to two years worth of emergency funds.

How much can you take?
To determine an appropriate withdrawal rate, you'll need to consider your age, life expectancy, living expenses and rate of return on investments.

If you're generally healthy, have adequate savings and retire at age 65, most planners say you can safely begin with a 4 percent to 6 percent withdrawal rate during your first year of retirement. After that, build in cost-of-living adjustments each year to account for inflation.

For example, if you've got a portfolio worth $500,000, withdraw roughly $25,000 the first year, and add an additional $750 the second year (using the standard 3 percent inflation rate) and so on.

Assuming a conservative 8 percent return on your overall portfolio, that 4 percent to 6 percent withdrawal rate will allow you to draw only from earnings without depleting your principal.

If you retire early, you will not only require a larger nest egg to cover your living expenses for longer, but may have to reduce your withdrawal rate by 1 percent to 2 percent.

"Inflation is a bigger factor for early retirees because it erodes your assets over time," says Balcom. "Some people go into retirement thinking they should invest heavily in certificates of deposit or bonds because they get a guaranteed return, but they don't understand that with taxes and inflation, there's no real return. You need to continue investing so you don't run out of money, especially if you plan to spend more than 30 years retired."

Regardless of age, he adds, all retirees should have a financial safety net in place to cover their living expenses for at least 12 months (ideally two years) and continue to strive for an 8 percent to 12 percent investment return.