The Internal Revenue Service explains the rules for required minimum distributions from individual retirement accounts on its website and provides worksheets to assist retirees with calculating their mandatory distributions using their IRA account balance, age and spouse's age. As of 2015, most IRA owners have to begin withdrawing funds from their accounts by April 1 following the year in which they reach age 70 1/2.
The required minimum distribution is the account balance divided by the distribution period, explains the IRS. Account owners must calculate their minimum distributions each year, and withdrawing more than the minimum does not offset future year required distributions. The IRS establishes three different tables to figure the factor by which IRA owners divide their account balances to determine their required distributions.
An account owner determines his distribution period according to his age in context with his spouse's age and beneficiary status, according to IRS Publication 590-B. Unmarried people use Table III to determine their withdrawal factors. A married IRA owner uses Table II to figure his withdrawal factor if he is married to a sole beneficiary more than 10 years his junior and Table III if his spouse is not his sole beneficiary or if his spouse is fewer than 10 years younger than he is. Table I applies to beneficiaries of deceased IRA account owners.