An additional issue impacting the IRA basis is whether your contributions were deductible or non-deductible. I did not see any of the other responses addressing this. Your contributions add to your basis only to the extent that they are non-deductible. And it only matters in that when you withdraw, the non-deductible contributions are not-taxable on a pro-rata basis (the portion they represent of the fair market value of your account). Maybe a change from being deductible to non-deductible (or vice-versa) is what is making you think the system messed it up? (just speculating). Not sure how many of your recent years of returns you have on your computer that you can access. There is a IRA information worksheet buried in the system that tracks your IRA basis (not just the 8606 form when it is produced). If you know what your all your contributions were (and you could potentially confirm this from the IRA custodians), and you know they were all non-deductible, and you have not done any withdrawals are, then you know what your basis is.
