Hi, yes you are correct. In general, you must begin withdrawing money by April 1 of the year following the year that you turn 70½.
While I am pulling up an excellent overview of the formula and it's logic, you may want to take a look at this: http://apps.finra.org/Calcs/1/RMD
For calculating your first year's distribution, the IRS specifically states to use your age on your birthday in the year you turn 70 1/2. For example, if your birthday is XXXXXXX January 1st and June 30th, the first year of distribution would be at age 70. If your birthday is XXXXXXX July 1st and December 31st, the first year of distribution would be at age 71.
Your required minimum distribution is the minimum amount you must withdraw from your account each year.
If you want to calculate the amount by hand IRS provides worksheets ... and you will use on of two different tables, depending on your situation; if your spouse is the sole beneficiary and is more than 10 years younger than you, you'll use the Joint Life and Last Survivor Expectancy Table ... FOr everyone else, use the Uniform Lifetime Table
Using the calculator I provided the link for, above ...
Sorry, that format transfer was atrocious, but to give you a fee, I used 1,000,000 and their required rate of return of 3.79% and age 70 as assumptions and that returned
The other assumptions I made were that your birthday occured on or before June 30th and that you were 70 years old ... this returned a withdrawal factor of 27.4
1,000,000 divided by 27.4 = 36,496 per year
Let me know if you have questions
Here's the IRS guidance on this: http://www.irs.gov/Retirement-Plans/Plan-Participant,-Employee/Retirement-Topics---Required-Minimum-Distributions-(RMDs)