Updated July 28, 2026. Quick answer: Never. Your own accounts and inherited accounts are entirely separate for this purpose — and inherited accounts from different decedents cannot be combined with each other either. Each stream is computed and taken independently.
Three separate universes
| Accounts | Aggregate together? |
|---|---|
| Your own IRAs | Yes, with each other |
| Your own IRAs + an inherited IRA | No |
| Inherited from Mum + inherited from Dad | No — separate decedents |
| Two inherited IRAs from the same decedent | Generally yes |
Someone who inherits from both parents and has their own IRA can be running three independent distribution schedules with three different calculations and three different deadlines — and no custodian sees more than one of them. This is where shortfalls happen, and each one attracts its own excise tax.
Different rules, not just different accounts
An inherited account may also require annual distributions inside a 10-year window — depending on when the decedent died — which is a different obligation from your own lifetime RMD, computed a different way.
Keep a single register
One sheet listing every account, its type, whose it was, and its annual requirement. It sounds trivial and it is the only thing that reliably prevents a shortfall across accounts nobody is looking at together.
Sources
IRC §401(a)(9) (required minimum distributions); IRC §408(d)(8) (qualified charitable distributions); IRC §4974 (excise tax on shortfalls, as amended by SECURE 2.0); SECURE Act (2019) and SECURE 2.0 (2022); final RMD regulations published 19 July 2024. Cross-checked July 2026 against professional analyses. Indexed dollar limits and correction windows are described rather than asserted.
This states what the cited authority says. It is not tax advice.