Mark retired and began receiving retirement income on May 1, 2016. No distributions were received prior to his retirement. Mark did not select a joint survivor annuity for these payments. Mark DOB-1-1-45. This is for 2016 tax return. Mark's 1099-R box 1-Gross Distribution $16,500.00. Box 2b is checked-(taxable amount not determined) Box 4 Fed tax withheld $1650.00- Box 7 distribution code(s) is 7- Box 9B Total employee contribution-$11,500.

How much of the $16,500 gross distribution reported on Form 1099-R is taxable in 2016?

I am using taxslayer software, does that help? If not it's ok thanks anyway.