Box 11 has two purposes. One is for reporting the amount of distributions made from the nonqualified plan, which is probably the most common use, and is an amount that is includible in income. The other is for reporting vesting of amount previously deferred and employer contributions previously made that are now vesting, making them subject to Social Security and Medicare taxes, an amount that is not includible in income. This is why TurboTax requires distinguishing between the two.
