I get a 1099-R as a pension as a check every month. my 1099-R box 2a taxable amount, .00. box 2b taxable amount not determined. used total as taxable, is this correct?

[robbaway13]

its from my deceased husband. How do I know what's taxable? Isn't it the full amount?

[MarilynG1]

Yes, usually the full amount in Box 1, Distribution, is also the taxable amount.  Some plan administrators check the 'taxable amount not determined' because they don't know what your other income is or how it affects taxability. 

A 1099-R is a distribution from a Retirement Plan, and those plans were normally made by pre-tax contributions, which is why they are taxable when distributed.  A Roth IRA being the exception to this rule, as tax was already paid on those funds.

Here's How to Enter a 1099-R.