As part of your participation in a 403(b) plan, the IRS will require you to make to begin taking required minimum distributions by April 1st of the year following the calendar year in which you turn 70.5 years old. 

The only exception is if the 403(b) plan permits, and the employee is still employed, they can defer the required minimum distributions until the year after they have retired. This option is not available to those employees who own more than 5% of the company.

The reason is simple - the purpose of a 403(b) account is for you to save for retirement. The Government doesn’t want the wealthy to be able to stock away large amounts of capital without ever paying taxes on the gains. 

This is one of the reasons that it is often advisable to have a Roth IRA in addition to a 403(b) account. The Roth IRA will never be subject to taxes meaning that if you find the next Microsoft or Berkshire Hathaway, every penny stays in your family.

You will be required to begin taking required minimum distribution 403(b) withdrawals in an amount specifically calculated so that the entire balance of your assets within the retirement plan will be distributed to you by the end of your life expectancy. 

It may sound morbid, but an accountant will actually help you break out the actuarial tables and calculate when you are likely to pass away, using the number of years of life left as a guide to coming up with a precise figure the IRS is likely to support.

In some cases, you can use the life expectancy of the designated beneficiary of the 403(b) plan, as well, which could be longer in the case of a married couple where one spouse is substantially younger than the other.

If you do not take your required minimum distribution 403(b) withdrawals, the IRS will penalize you with a 50% excess accumulation tax.