Unfortunately, there's usually a 10% penalty—on top of the taxes you owe—when you withdraw money early. This is where the rule of 55 comes in. If you turn 55 (or older) during the calendar year you lose or leave your job, you can begin taking distributions from your 401(k) without paying the early withdrawal penalty.

At age 59½, you can withdraw both contributions and earnings with no penalty, provided that your Roth IRA has been open for at least five tax years.

If you convert a traditional IRA or 401(k) to a Roth IRA , you'll need to hold the Roth IRA for at least five years before making withdrawals to avoid the 10% early withdrawal penalty and be age 59 ½ or older. The five-year period starts on the first day of the tax year in which you made the conversion.

This rule for Roth IRA distributions stipulates that five years must pass after the tax year of your first Roth IRA contribution before you can withdraw the earnings from the account tax-free. Keep in mind that the five-year clock begins ticking on Jan. 1 of the year you made your first contribution to the account.

One frequently used rule of thumb for retirement spending is known as the 4% rule. It's relatively simple: You add up all of your investments, and withdraw 4% of that total during your first year of retirement. In subsequent years, you adjust the dollar amount you withdraw to account for inflation.