Payroll has to run on the first Friday.

What HR and payroll need on Day One.

Day One needs an employee master file with every Newco employee accurately reflected. The file needs accurate compensation, tax withholdings, benefit elections, direct deposit instructions, work location, and employment status. Errors in any field surface in the first pay run as either underpayment or overpayment. Both create employee friction and remediation work. The master file is the artifact most likely to cause downstream pain when wrong.

Day One needs an active payroll platform that can process the first pay run on schedule. The platform must be loaded with the employee master, configured for Newco tax registrations, integrated with the time and attendance system, and connected to the Newco bank account funding payroll. Each component has its own setup time. The platform readiness date typically needs to fall two to four weeks before the first pay run for testing.

Day One needs employee benefit coverage that is at least as good as the seller's coverage. COBRA notifications, plan transitions, and election windows all have regulatory clocks. Health insurance gaps create immediate employee grievances and potential liability. Retirement plan transitions require careful handling of vested balances, deferral elections, and plan documents. The benefits decisions need to be made months before close.

Day One needs working employee identification, payroll deductions correctly configured, garnishment orders properly transferred, and state tax registrations active in every jurisdiction where Newco employs anyone. Each item has its own clock. The HR workstream needs to map every clock and back schedule from close. The broader Day One picture is in carve-out Day One readiness.

The three platform paths every buyer considers.

Path one is stay on the seller's HRIS and payroll through the TSA. Newco operates on the seller's platforms with a sublicense or a managed service arrangement. The path is fast to set up and predictable in the short term. It carries TSA pricing pressure, data segregation risk, and dependency on the seller's IT operations. It also requires careful handling of payroll tax filings because the seller is filing on a different employer identification number than Newco's.

Path two is move to a Newco instance of the same platform. If the seller uses Workday, Newco stands up its own Workday tenant. If the seller uses ADP, Newco contracts directly with ADP. This path preserves user familiarity and process continuity. It carries the highest licensing flexibility and the cleanest separation. It typically takes 4 to 8 months to implement depending on complexity and is the path most carve-outs ultimately follow.

Path three is move to a different platform appropriate to Newco scale. Newco selects a new HRIS and payroll provider sized for its operating profile. The path produces a cleaner long term cost structure and a system designed for Newco rather than inherited from the seller. It carries the highest change cost in user training, process redesign, and data migration. It typically takes 6 to 12 months and works best when Newco is materially smaller than the seller.

The decision rule mirrors the ERP decision but on a faster clock. The HR and payroll decision often needs to be made before the ERP decision because the lead times are shorter and the Day One pressure is harder. Choosing path one as a deliberate bridge to path two or path three is a common pattern. Choosing path one as a permanent state is rarely a good outcome.

The regulatory clocks that drive the schedule.

Federal and state payroll tax registrations take 4 to 12 weeks depending on jurisdiction. Newco needs an employer identification number, state unemployment insurance registrations in every state of employment, state withholding registrations, and local tax registrations where applicable. The Form SS-4 for the federal EIN can be processed quickly but the state registrations vary in speed. Some states require Newco to have a registered agent and active corporate registration before unemployment insurance opens.

Health insurance carrier transitions take 60 to 120 days. New carrier contracts require underwriting, plan design selection, network confirmation, and member enrollment. Carrier transitions tied to a Day One effective date require carrier agreement to a fixed start date. Carriers will not always agree to dates that align with close, particularly when the carve-out perimeter changes shape during negotiation. Backup options need to be in place.

Retirement plan transitions are tightly governed. A new 401(k) or pension plan requires plan documents, recordkeeping selection, custodian contracts, ERISA compliance review, and participant communications. The IRS rules around plan terminations, asset transfers, and successor plans are unforgiving. Errors create plan disqualification risk. The retirement plan decisions need to be made early and confirmed in writing with the seller before signing.

International payroll adds another layer. Each country has its own statutory requirements, social security registrations, works council notifications, and data privacy rules. Cross-border carve-outs need country by country playbooks with local counsel and local payroll providers. The cross-border picture is detailed in cross-border TSA considerations.

Data migration and the first pay run.

The employee master file migration is the work item most likely to cause first pay run failures. Source data lives in the seller's HRIS, often with custom fields, legacy attributes, and inconsistencies that accumulated over years. The mapping to the target system requires field by field translation, validation against payroll requirements, and reconciliation against the source. Programs that take master file accuracy for granted produce expensive first pay runs.

Year to date balances need careful handling. If Day One falls mid year, every employee carries year to date wages, taxes withheld, and benefit deductions that need to migrate to Newco's payroll system. The migration ensures W-2s are correct at year end. Sellers will sometimes resist providing year to date data on the grounds of complexity. The buyer needs to require it in the TSA and confirm the format in advance.

Parallel pay runs are the safest test. The week before go live, Newco's new payroll system processes a parallel run against the seller's actual production payroll. The two outputs reconcile employee by employee, deduction by deduction, tax by tax. Discrepancies surface before the live run. The parallel pattern adds two to four weeks to the timeline and is worth every day.

The first live pay run is the moment the program either ships or fails. The bank account must be funded, the ACH file must be released on schedule, the tax filings must be initiated, and the pay stubs must be available to employees. Programs that rehearsed the run and tested the integrations usually ship cleanly. Programs that left the first run to discover its problems usually deal with employee grievances for weeks. The finance integration is in Day One finance readiness.

Talent risks around the deal.

Carve-out announcements create employee uncertainty. The best employees often receive recruiting outreach within days of the announcement. Retention bonuses, equity replacement programs, and clear communication about Day One arrangements reduce attrition during the window. Programs that wait to communicate until Day One usually lose more talent than necessary. The retention budget should be set during diligence and deployed at announcement.

Shared services employees are a particular concern. Many seller employees who supported Newco operations remain with the seller after close. The TSA provides their services through Day One and through the exit ramp. The seller has limited incentive to retain those employees through the full TSA. Knowledge transfer programs, embedded resources, and replacement hiring on the Newco side need to be planned from signing rather than scrambled mid TSA.

Compensation harmonization is a multi quarter project. Newco often inherits seller compensation philosophies, pay ranges, and incentive structures that do not match the operating partner's value creation plan. Realignment requires careful change management to avoid grievances and unintended attrition. The first compensation review under Newco governance is usually 6 to 12 months after Day One. The program needs an interim approach that holds the workforce steady until then.

Works councils, unions, and statutory employee representatives have rights that vary by country. In some jurisdictions, the transaction itself requires consultation with employee bodies. In others, post-close changes to working conditions trigger consultation rights. The legal complexity is real and the timelines are often longer than buyers expect. Local counsel needs to be engaged early in every jurisdiction with employee representation.

More on carve-out execution.