What Does it Mean if "Taxable Amount Not Determined" in Box 2b on Form 1099-R is Checked?

If the first box in 2b, "Taxable Amount Not Determined," is checked, that means the payer was uanable to determine the taxable amount of your distribution. Unless the distribution is from an IRA, if box 2b is checked, box 2a should be blank. It is the recipient's responsibility to determine the taxable amount.