Per the IRS tax code, a "required minimum distributions apply each year beginning with the year the account owner turns age 70 1/2. According to the IRS rules, "the required minimum distribution for each year is calculated by dividing the IRA account balance as of December 31 of the prior year by the applicable distribution period or life expectancy."
A IRA owner may be able to determine "his or her applicable distribution period or life expectancy by using the Tables in Appendix C of Publication 590." (Click on this link http://www.irs.gov/pub/irs-pdf/p590.pdf
1. Table I is used by beneficiaries.
2. Table II is for use by owners who have spouses who are both the IRA's sole beneficiary and who are more than 10 years younger than the owner.
3. Table III is for use by all other owners.