How to keep a tax-loss-harvesting agent from voiding a loss in an IRA

This month Interactive Brokers wired Claude directly into client accounts. The agent drafts a trade, the client approves it in an AI Instructions tab, and it goes to market. Robinhood and a handful of others opened similar bring-your-own-agent rails the same week. The feature that follows close behind, on every one of these platforms, is automated tax-loss harvesting: let the agent sell the losers, book the loss against gains, and hold the same market exposure through a near-identical fund. It is a genuinely useful chore to hand off. The question worth asking before we hand it off is narrow and expensive: does the agent see all of our accounts, or only the one it is wired into?

How fast an automated harvesting agent acts

The rails are real and they are fast. As FinTech Global reported this month:

That speed is the point and also the hazard. A harvesting agent is built to act the moment a position goes red, and it acts inside whichever account holds the API connection. Meanwhile the rule it has to respect spans a wider perimeter than its own login. 24/7 Wall St walked through a clean version last month: a retiree sold roughly $300,000 of a total-market fund at a $90,000 loss, and two weeks later a scheduled dividend reinvestment inside her IRA quietly bought about $9,000 of the same fund. That single automatic purchase disallowed $9,000 of the loss, 10% of the harvest, costing her $2,430 in real tax at a 27% combined rate. No agent was even involved. A dividend setting did it.

The wash-sale rule spans every account, not one login

Here is the part most harvesting pitches skip. The wash-sale rule disallows a loss if a substantially identical security is bought within 30 days before or 30 days after the sale, a 61-day window, and the Internal Revenue Service computes that across every account one taxpayer controls: taxable, IRA, 401(k), and a spouse’s accounts too. An agent watching one account is structurally blind to a buy in an account it never connected to.

The sting is what happens next, and it splits two ways.

In a taxable-to-taxable collision the loss only goes to sleep: it rides along as extra basis on the replacement shares and comes back when those shares are sold. But the IRS settled in Revenue Ruling 2008-5 that when the offsetting buy happens inside a retirement account, Section 1091(d) refuses to raise the IRA’s basis, because a tax-sheltered account has no basis to raise. The loss is not deferred. It is destroyed.

What to do before letting an agent harvest

1. Inventory the whole household first

   List every account under one tax return: taxable, every IRA, the 401(k), and a spouse's accounts. The wash-sale perimeter is the list, not the login.

2. Kill automatic reinvestment in any account you harvest in

   Turn off dividend reinvestment on funds being harvested, in every account. A scheduled reinvestment is an automated buy the agent cannot see.

3. Confirm the agent's actual scope

   Read what the connection can see. A single-account agent does not know your IRA exists, so it cannot warn you about a collision there.

4. Keep a 31-day no-buy list

   When a loss is harvested, the same fund and any substantially identical fund are off-limits across all accounts for 31 days, including auto-rebalancing.

5. Never let the replacement land in a retirement account

   If a near-identical fund must be repurchased, route it to a taxable account, where a collision only defers the loss instead of voiding it.

6. Reconcile in January, before filing

   Cross-check realized losses against every account's January activity. The disallowed slice shows up on the broker's sales-reporting form only for the account that sold, never the one that bought.

The agent is good at the part it can see and oblivious to the part it cannot. That is not a reason to avoid it. It is a reason to draw the perimeter ourselves before we let it start selling.