How to switch HRIS providers without breaking payroll

An HRIS migration goes wrong in one of three places: the data audit nobody scoped, the parallel payroll run nobody scheduled, or the carrier feed cutover nobody owned. Get those three right and the rest is project management.

Before you sign anything: the data audit

Most teams budget for the new system and skip the cost of cleaning up the old one. Don't. Before contracts get signed, pull a full export from your current HRIS and answer:

• ›How many employees have incomplete tax forms, missing direct deposit info, or stale emergency contacts?
• ›Are comp histories continuous, or are there gaps where merit cycles got loaded as new records?
• ›Do your job titles, levels, and cost centers match across HRIS, payroll, and finance? (They almost never do.)
• ›How many active integrations push or pull from the current system, and who owns each one?

Every gap you find now is a gap you fix in the old system before migration. Every gap you skip becomes a ticket on go-live week.

The realistic timeline

Vendors will quote 8 to 12 weeks. For a 200 to 500 person company with payroll, benefits, and at least two integrations, plan on 14 to 20. Here's where the weeks actually go:

• ›Weeks 1 to 3: Data audit and cleanup in the old system.
• ›Weeks 3 to 6: Configuration in the new system — fields, workflows, permissions, integrations.
• ›Weeks 6 to 10: Data migration, validation, and reconciliation. Plan two full dry runs.
• ›Weeks 10 to 12: Parallel payroll run. Net pay must match to the penny.
• ›Weeks 12 to 14: Benefits carrier feed cutover, EDI test files, and 834 validation.
• ›Weeks 14+: Go-live, hypercare, and the issues you didn't predict.

Run payroll in parallel. No exceptions.

At least one full pay cycle should run in both systems with the same inputs, and net pay must match to the penny before you cut over. If it doesn't match, you have a data problem — find it before employees do.

If your vendor pushes back on a parallel run because it adds time, that's a signal worth taking seriously. Parallel runs catch the mapping errors that turn into W-2 corrections in January.

Benefits carrier feeds: the silent killer

Payroll gets the attention. Benefits feeds get the post-mortem. EDI 834 files between your new HRIS and every carrier — medical, dental, vision, life, FSA, HSA — need to be tested, validated by the carrier, and signed off before you cut traffic over. Each carrier has its own timeline. Some take six weeks just to schedule the test.

Start the carrier conversation the day you sign the contract, not the week before go-live.

What to communicate, and when

• ›60 days out: Tell managers what's coming, why, and what they'll need to do.
• ›30 days out: Tell employees. Show them where to find their info in the new system. Record a short video.
• ›Go-live week: Slack-active war room. Don't push a new self-service flow the same week you cut over.
• ›30 days post: Retro with HR, payroll, IT, and finance. Capture what you'd do differently.

The Tallo angle

We've run this playbook with teams switching off Workday, UKG, ADP, BambooHR, and Rippling. The pattern holds. The teams that go smoothly are the ones that respect the data audit and budget for the parallel run. The teams that struggle are the ones that trust the vendor's optimistic timeline.

If you're scoping a switch and want a no-nonsense second opinion on the timeline, we're happy to walk through your situation. No pitch deck required.