Starting in April of the year after you reach age 70-1/2 you have to take a minimum withdrawal amount as determined by the IRS. Depending on your age and the ages(s) and of your beneficiary(ies), there is an assumed number of years that you (or your benficiary) will be withdrawing funds - so you divide the amount in your account by that number of years. For someone age 70 whose sole benfecary is a spouse whose age is within 10 years of the account owner, the distribution period is assumed to be 27.4 years, so that year you must take a minimum distributions of 1/27.4 = 3.65%. Here's the table: IRA minimum distributions table