Can anyone tell me what the basis of retirement is if the cash distribution was an RMD?

[DaveF1006]

The basis is the amount of money paid in to the retirement account prior to distributions.

[Opus 17]

Basis is the amount of already-taxed money that was paid into the account.

For example, you generally have zero basis in a defined pension (because the employer funded it with tax-free money), and you generally have zero basis in a pre-tax IRA, 401k or other plan (because the money was deducted from your pay pre-tax, you never paid tax on it.)

You might have a basis if you made non-deductible contributions to a traditional IRA, but you need to have kept copies of your old form 8606s to prove it.  Your basis in a Roth IRA is the amount of your original contributions because they were all made after tax.