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This post uses hypothetical scenarios for illustrative purposes only. It does not describe any actual client, transaction, or representation, and is not legal advice.

Take a typical stock-sale situation: a forty-employee company, a healthy 401(k) with a safe harbor match, and a buyer whose benefits counsel sends over a covenant that reads like an execution order — the target shall adopt resolutions terminating its 401(k) plan effective no later than the day immediately preceding the closing date. Imagine the founder reading that for the first time. The plan is fine. The employees like it. Why would anyone insist on killing a perfectly good retirement plan the day before the wire hits?

The answer is one of the least intuitive rules in deal work, and it has a name that sounds like it was invented to be skipped over: the successor plan rule. Founders who understand it stop arguing about the covenant. Founders who don’t sometimes cost their buyer — and their employees — the ability to ever cleanly unwind the plan.

In a stock sale, the buyer inherits the plan with everything in it

Start with why the buyer cares. In a stock purchase, the target survives as an entity, and everything it sponsors comes along — including the 401(k), and including every operational mistake ever made inside it. Late deposits of deferrals, a definition of compensation the payroll system never matched, a missed amendment from two administrations ago: qualification defects don’t stay behind with the sellers. They ride the stock certificates into the buyer’s controlled group, and if the target plan is later merged into the buyer’s plan, they can taint the buyer’s plan too.

So buyers make a structural choice, and they make it before signing. Either the target’s plan is terminated before closing and the buyer never sponsors it, or the buyer keeps it alive for a transition period and merges it later after a full protected-benefits analysis. As firms like Morgan Lewis have , pre-closing termination is the default preference in most middle-market stock deals, and the reason is timing that cannot be recreated after the fact.

The successor plan rule gives you exactly one clean window

Here is the mechanic. A 401(k) plan that terminates can generally pay out participant accounts — that’s what lets employees roll their balances into the buyer’s plan or an IRA and lets the old plan actually die. But the Treasury regulations under section 401(k) contain a trap: if, at the time of termination, the employer (measured across the whole controlled group) maintains another defined contribution plan, the terminated plan generally cannot distribute elective deferrals at all, unless fewer than two percent of the target’s employees are eligible for the other plan during a window running from twelve months before termination to twelve months after.

Now run the timeline both ways. Terminate the day before closing, while the target is still its own controlled group with one plan, and there is no successor plan in the picture — distributions are permitted, employees get a distributable event, balances roll where the employees choose. Wait until the day after closing, and the target now sits inside the buyer’s controlled group, which almost certainly maintains its own 401(k). That buyer plan is a successor plan. Terminating the target plan now produces a plan that is dead but cannot pay anyone out — deferrals, safe harbor contributions, QNECs and QMACs are all locked in until each employee separately earns a distributable event: termination of employment, age 59½, hardship, disability, death. The plan becomes a zombie: frozen, still filing Form 5500s, still generating fees, still capable of compliance failures, mergeable only after an anti-cutback analysis that preserves every protected benefit it ever promised.

One day on the calendar. That’s the entire difference.

The covenant is boilerplate; the sequencing is not

What does executing this well actually look like? First, the board of the target adopts termination resolutions before closing — typically effective the day immediately preceding the closing date, and drafted so the termination is contingent on the closing actually occurring, so nobody has killed the plan if the deal dies on the courthouse steps. Second, the termination triggers full vesting of employer contributions for affected participants, which is required on termination and should be modeled in the deal economics rather than discovered afterward. Third, the recordkeeper needs real lead time — termination amendments, blackout notices, and distribution paperwork are not same-week deliverables, and a recordkeeper hearing about the deal at closing is a recordkeeper who will miss the window. Fourth, outstanding participant loans need a plan of their own: if the buyer’s 401(k) will not accept rollovers of loan notes, employees face a choice between repaying and defaulting, and that is an employee-relations conversation someone should have before closing day, not after.

The founder’s instinct — the plan is good, why kill it — deserves an honest answer on the other side too. Termination means distribution events for the whole workforce, and some employees will cash out and spend rather than roll over. The industry calls it leakage, and it is the real cost of the clean path. The alternative — buyer keeps the target plan alive, then merges it — preserves account continuity and avoids loan disruption, but it imports every historical defect into the buyer’s plan, requires the protected-benefits analysis, and leaves the buyer running two plans with two testing cycles in the meantime. There is also a modest grace period in the coverage rules for deals like this — the transition relief generally runs through the end of the plan year following the year of the transaction — but it postpones the reckoning; it doesn’t cancel it.

Asset deals flip the problem

In an asset sale, none of this drama shows up, because the plan sponsor doesn’t change hands. The 401(k) stays with the selling entity, which winds it down on its own schedule after closing. The hired employees terminate employment with the seller — a distributable event on its own — and enroll in the buyer’s plan as new hires. The seller’s job is the wind-down: final contributions, vesting, distributions, final Form 5500. The buyer’s job is making sure eligibility and enrollment are ready on day one so the workforce doesn’t sit uncovered. It is the same reason benefits diligence looks different by structure — a theme that runs through benefits diligence generally, where COBRA and ACA obligations also allocate differently between asset and stock deals.

Where this lands for a founder

The 401(k) covenant usually arrives in the same draft as the provisions founders actually read closely — the treatment of stock options at closing, the vesting acceleration triggers — and it gets a fraction of the attention because it doesn’t move the purchase price. But it moves three things founders care about. It fixes a board action to a specific day that cannot slip. It creates a workforce communication moment — forty employees learning their retirement plan is terminating is how forty employees learn the company is being sold, so the announcement sequencing belongs in the deal timeline. And it allocates wind-down costs and responsibilities that will otherwise default to whoever wasn’t paying attention.

The likely outcome, when the sequencing is respected, is genuinely boring: resolutions adopted the day before closing, balances rolled over a few weeks later, the old plan filing its final return the following year. Boring is the goal. The successor plan rule only becomes interesting when someone misses the window — and it only takes one day to miss it.

If you are working through what happens to a 401(k) on either side of a company sale, feel free to reach out to my firm manager, Magda, at Magda@montague.law, or fill out our contact form. Mention you read this post.