The day-one payroll integration playbook for acquirers.
The transition service agreement runs 90 days. The integration architecture has to be usable on day one. Here is the playbook we run for acquirers of mid-market and enterprise targets.
The four decisions the deal team owes payroll.
Post-close payroll architecture is determined by four decisions the transaction team typically makes before payroll is consulted. When they are made in the right order, day-one integration is routine. When they are not, the first pay cycle after close surfaces problems that take quarters to unwind.
- Legal entity structure — does the acquired workforce move to the buyer's Federal Employer Identification Number, or does the target's entity survive?
- Successor-employer treatment — will the transaction qualify as an acquisition of the trade or business under Internal Revenue Code Section 3306(b)(1) for FUTA and under each state's successor-employer rules for unemployment?
- Benefits continuation — do target employees remain on the target's benefits through the plan year, or are they enrolled in the buyer's plans on day one?
- Payroll platform — does the target's workforce move to the buyer's payroll platform immediately, remain on the target's platform through a transition services agreement, or run in parallel on both?
Day one — what must be true.
- Every state, local, and special-purpose district with target-side wages is registered under the surviving entity, with account numbers issued and deposit schedules confirmed.
- Successor-employer paperwork is filed with every state where the transaction qualifies. Where it does not qualify, new employer accounts are open and rated.
- Federal Employer Identification Number is confirmed for the entity that will report wages after the close date. If a new one is needed, it is issued.
- Workers' compensation coverage is in force in every state on the effective date, with no gap from the target's prior coverage.
- The first pay cycle's tax deposits are calendared, with clear ownership of which entity deposits which portion when the close date falls mid-cycle.
The nexus map is the entire integration.
Every subsequent step depends on the accuracy of the nexus map. Missed jurisdictions surface as notices six to nine months after close — usually first from Pennsylvania Act 32 collectors, Ohio RITA locals, and Oregon transit districts. By the time the notice arrives, the assessment has accrued penalty and interest, and the response window is compressed.
We build the map from the target's employee census, cross-referenced with the target's filing history and remote-worker records. Any state with wages and no filing history goes on the exposure list immediately.
The first pay cycle after close.
The first cycle is not the celebration. It is the audit. Every jurisdiction's deposit must clear, every deduction must reconcile against the target's final calculation, and every employee must be able to see their pay stub with the correct entity, the correct rate, and the correct year-to-date figures.
We run the first cycle in parallel with the target's payroll platform when possible. Reconciling gross-to-net across both systems catches conversion errors before they hit the employee.
The year-end reconciliation.
In the calendar year of the close, target employees will receive wages under two Federal Employer Identification Numbers — the target's and the buyer's. Whether Social Security, Medicare Additional, FUTA, and state unemployment wage bases carry over depends entirely on the successor-employer determinations made during registration.
The reconciliation is the buyer's obligation. Skipping it produces over-withheld Social Security (refundable to employees via Form W-2c), over-deposited FUTA (refundable via Form 940 credit-reduction reconciliation), and mismatched state unemployment reporting (potentially triggering state-level notices in the year following the transaction).
Questions we get on this one.
- When should payroll integration planning start?
- At signing, at the latest. Registration lead times in the higher-friction states (Pennsylvania, New York, California, Ohio) can run six to eight weeks. Starting at close guarantees the first pay cycle runs before every account is issued.
- Do the target's employees need new Federal I-9s and W-4s?
- Only if the acquiring entity is a new employer under Internal Revenue Code and Immigration and Nationality Act rules — typically an asset purchase where the target's entity does not survive. In a stock purchase where the target's entity survives, existing I-9s and W-4s remain valid.
- Can we transfer the target's state unemployment experience rating?
- In most states, yes — under the state's successor-employer rules when the transaction qualifies as an acquisition of the trade or business. In others, the experience rating is mandatory to transfer under the state's SUTA-dumping prevention statutes, and the buyer must accept it whether favorable or not.
- How do we handle 401(k) plans post-close?
- Three paths: continue the target's plan under the surviving entity, merge the target's plan into the buyer's plan, or terminate the target's plan and enroll employees in the buyer's plan. Each has plan-document, notice, and testing consequences. The choice should be made 60 to 90 days before close.
Day-one integration is an architecture problem.
Every registration, every deposit calendar, every reconciliation. Sequenced before the close, executed on day one.