Payroll has to run on Day One. No exceptions.

Provider decision and the tenant strategy.

The first decision is whether Newco stays on ADP or moves to another provider. Workday Payroll, UKG, Paychex, Paylocity, and country specific providers all compete for the new logo. The decision rests on country footprint, integration with the Newco HRIS, total cost of ownership, and operational fit for Newco scale. The case for staying on ADP is continuity. The case for switching is fit. Both are valid in different fact patterns.

If Newco stays on ADP, the tenant strategy still requires work. ADP serves enterprise customers through several product lines including ADP Workforce Now, ADP Vantage HCM, and ADP GlobalView Payroll. The seller may run one product. Newco may need a different one. The conversation with ADP covers product selection, the implementation timeline, and the commercial terms for a net new contract under the Newco legal entity.

If Newco switches providers, the program is larger but the leverage is also larger. The new provider treats Newco as a competitive deal. Pricing softens. Implementation hours get bundled. Customization scope expands. The Newco team prepares a payroll requirements document covering country footprint, pay cycle, deduction codes, garnishments, time integration, expense integration, and reporting needs. The document drives both the selection and the contract.

The TSA period covers the gap between Day One and the Newco production payroll cutover. Newco runs payroll on the seller ADP tenant under a documented service catalog with a known exit date. The pricing follows the same cost-plus discipline the rest of the TSA uses. The work aligns with the TSA exit HR payroll separation sequence.

Tax registrations and the legal entity work.

Payroll requires legal entity registrations in every jurisdiction where Newco employs people. Federal Employer Identification Number in the United States. State unemployment insurance accounts. State withholding accounts. Local tax accounts in jurisdictions that levy them. Workers compensation policies. Disability insurance accounts in states that require them. Each registration has a lead time. None of them complete on the day they are filed.

International registrations are harder. PAYE in the United Kingdom. CRA payroll accounts in Canada. URSSAF accounts in France. Each country has its own filing schedule, its own electronic filing requirements, and its own penalty structure for late or missed filings. The Newco legal and tax team starts these registrations months before the production cutover. The work pairs with the Day One legal entity setup workstream.

ADP requires the new account numbers before it can run payroll for the Newco entity. The provider implementation team validates the registrations against jurisdiction databases. Missing or pending registrations block the production go live. The Newco team builds the registration tracker as a critical path artifact and reviews it weekly with the legal entity setup workstream lead.

The Successor Employer election in the United States is a separate decision. The election allows Newco to inherit the seller wage base for Federal Insurance Contributions Act and Federal Unemployment Tax Act calculations within the same calendar year, which reduces double taxation on transferred employees. The legal team confirms whether the carve out structure qualifies and files the election within the regulatory window.

Employee file transfer and data quality.

The employee file is the master extract from the seller ADP tenant. Personal data, employment data, pay data, tax withholding elections, direct deposit accounts, deduction elections, benefits enrollments, time off balances, and year to date earnings. The extract is structured to the new ADP tenant import format. Each field maps explicitly. Each transformation rule is documented. The mapping document is the artifact that audit will ask for two years later.

Data quality issues surface immediately. Inactive employees that were never terminated in the seller system. Duplicate records for the same person across business units. Missing tax withholding forms. Garnishment orders that have expired but were never closed. Direct deposit accounts that have been closed at the bank. Each issue is triaged by the people operations team before the file enters the new tenant. The cleanse is real, not cosmetic.

Year to date earnings carry weight. For employees transferred mid year, year to date wages, year to date tax, year to date deductions, and year to date employer paid amounts all migrate. The transfer protects the employee from over withholding and protects the employer from incorrect year end reporting. The new ADP tenant validates the year to date load before activating the employee for production payroll.

Sensitive data handling is documented end to end. The extract travels over encrypted channels. The intermediate files live in access controlled storage. The new tenant ingests the data behind multi factor authentication. The people operations team and the technology team sign off on the data handling before the first record moves.

Parallel payroll and the cutover plan.

Parallel payroll is the test that determines whether the new tenant is ready for production. The Newco team runs at least two and ideally three full payroll cycles in parallel. The seller tenant produces the live payroll that pays employees. The new tenant produces a shadow payroll on the same employees, the same pay period, and the same inputs. Every variance is investigated and resolved before the next cycle.

Variance categories repeat across implementations. Tax calculation differences from jurisdiction setup errors. Deduction code mapping differences. Benefits contribution differences from plan configuration. Time integration differences from rule translation errors. The work is patient. The acceptance criterion is a parallel cycle with zero unexplained variances at the employee level.

The cutover weekend is sequenced around a pay date. The final production payroll runs on the seller tenant. Final year to date balances export. The new tenant ingests the final balances. The first production payroll on the new tenant runs against those balances. The discipline avoids the catastrophic case where an employee gets paid twice or not paid at all on the first new tenant cycle.

Communication is structured. Employees receive a clear timeline of what will change, what will not change, and what they have to do. Direct deposit accounts do not have to change. Tax withholding forms may need re submission depending on jurisdiction. Pay statements may look slightly different. The discipline reduces the volume of inbound questions to the people operations team during the most sensitive week.

Cost discipline and year end close.

Payroll separation programs typically run between $300K and $1.5M depending on employee count, country footprint, time integration complexity, and benefits integration scope. The economics hold when the implementation statement of work is tight, the data cleanse is real, and the parallel payroll cycles are completed before the cutover date is committed. Where any of those three slip, costs and risks escalate.

Year end close is the second risk event after the cutover. The W-2 forms in the United States, the T-4 forms in Canada, the P-60 forms in the United Kingdom, and the equivalent country specific forms have to reconcile across the seller tenant and the new tenant for any employee transferred mid year. The reconciliation runs from the year to date data migration document and the parallel payroll archives. The work starts in November for a January year end.

Most common timeline slips trace to delayed tax registrations, late discovery of garnishment orders, and unresolved parallel payroll variances. The fix is the disciplined registration tracker, the early garnishment audit, and the absolute rule that no cutover is approved until the parallel cycle has zero unexplained variance. Where the discipline holds, Day One pay is uneventful.

A clean payroll separation produces a Newco that runs its own payroll, its own tax filings, its own year end forms, and its own service relationship with the provider. The program is delivered under a Fixed Fee + Portfolio Retainer engagement model through TSA exit acceleration.

More on platform separation.