The "plan cost" information is not provided by my pension provider (the Wisconsin Retirement System). How do I answer the "Plan cost" question?

[Brillig]

I had 38 years in the system and retired 5 years ago.

[AnnetteB6]

The plan cost represents any amount that you contributed to the plan with after-tax funds.  If you did not make any after-tax contributions, then your plan cost will be zero.  

The plan cost may be reported on Form 1099-R in box 9b, but generally only in the first year that you receive a distribution from the plan.  

Without some sort of documentation for the plan cost, you will need to enter zero in that box.  This will make your distribution fully taxable, which is the most common situation. 

[Brillig]

The 1099-R provided by the Wisconsin Retirement System does include both a gross distribution amount in Box 1 and a taxable amount in Box 2a. I have entered that information into TurboTax.  Perhaps TurboTax does not need the "plan cost" value filled in if the the gross distribution and taxable amounts are provided on the 1099-R. 

[JamesG1]

What 'plan cost' did you report on last year's tax return?

Box 9b Total Employee Contributions of the IRS form 1099-R may report the employee's cost in the plan.

IRS Instructions for IRS form 1099-R, page 16, reports the following about box 9b Total Employee Contributions:

Box 9b

Total Employee Contributions You are not required to enter the total employee contributions or designated Roth contributions in box 9b. However, because this information may be helpful to the recipient, you may choose to report them.

@Brillig 

[Brillig]

It is good to know that the plan cost data is not needed.  I did not think the information was needed since I have filled out this form on TurboTax Desktop version for many years.  The problem was the web based TurboTax required me to put in a number or my return was incomplete and I could not e-file. I ended up putting in a zero for that value and the software was ok with that.