Updated July 28, 2026. Quick answer: Ranked by cost rather than frequency: naming the estate or leaving the form blank, a stale ex-spouse, splitting “equally” by balance across accounts with different tax character, and assuming the will controls.
In order of damage
| Mistake | What it costs |
|---|---|
| Blank form or estate named | Five-year emptying instead of ten, probate, lost protections |
| Stale ex-spouse | The entire account, to the wrong person |
| No contingent beneficiary | Defaults to the estate; disclaimer planning becomes impossible |
| Equalising by balance | Substantially unequal after tax |
| Leaving the IRA to children and the brokerage to charity | Wastes the step-up and hands heirs the taxable asset |
| Assuming the will controls | The designation wins; the will is irrelevant here |
The audit that prevents most of them
- Request the current designation, in writing, from every custodian.
- Confirm both primary and contingent are named on each.
- Check per stirpes versus per capita reflects your actual intent.
- Compare after-tax value across accounts, not balances.
- Repeat after any marriage, divorce, birth, death or account transfer.
Every item on that list is free and takes an afternoon. Between them they prevent most of the expensive outcomes described across this cluster — which is unusual in tax, where most improvements cost something.
Sources
SECURE Act (2019); SECURE 2.0 (2022); final RMD regulations published 19 July 2024; IRC §401(a)(9); IRC §1014 (basis of property acquired from a decedent); IRC §664 (charitable remainder trusts). Cross-checked July 2026 against professional analyses from Kitces, Grant Thornton, Ascensus, Charles Schwab and Kiplinger. Indexed figures and state-specific rules are flagged rather than asserted.
This states what the cited authority says. It is not tax or legal advice, and beneficiary planning turns on family facts and state law that no page can see.