Why not replace the old ERP all at once?
A single cut-over asks every department to change how it works on the same day, with no easy way back if something breaks. For a business that has to keep invoicing, paying staff and shipping orders, that is a large and concentrated risk.
It also delays value. Nothing improves until everything is finished.
What does a staged modernisation look like?
The old system stays in place as the system of record while new capabilities are built alongside it. An integration layer keeps both in sync. One process at a time — procurement approvals, then inventory, then reporting — moves to the new platform, and the old module is retired only once the new one has run cleanly.
This is sometimes called the strangler pattern: the new system gradually takes over responsibilities until the old one has nothing left to do.
Where should you start?
Start where the pain is highest and the dependencies are fewest.
- Reporting is often a good first step. It reads from the core system but rarely needs to change it, and better reporting is visible to leadership quickly.
- Approvals and workflows are another. They sit around the ERP rather than inside it, and replacing email-based approvals has an immediate effect.
- Core finance and inventory usually come later, once the integration layer and data quality have been proven.
What has to be true before each step?
- The data for that process has been mapped and cleaned.
- The integration keeps both systems consistent, and any differences are reported.
- The people who run the process have used the new version on real work.
- There is a documented way to fall back.
How do you keep data consistent while two systems run?
Decide, for each record type, which system is the source of truth at each stage — and write it down. Customers might be owned by the old ERP until stage three, then by the new one. The integration layer enforces that ownership: changes flow from the owner to the other system, never both ways at once.
A daily reconciliation report comparing key totals between the two systems catches drift early.
What does it cost?
A staged approach usually costs more in integration work than a single cut-over would on paper, because both systems need to be connected for a period. In exchange, risk is spread out, value arrives earlier, and each step can be paused or adjusted based on what the previous one taught you.
Modernisation done this way takes longer to finish, but the business never stops to wait for it.