What is Parallel Adoption?
Parallel adoption runs the new ERP and the legacy system side by side for a period so results can be compared before retiring the old system.
Definition
Parallel adoption (or parallel running) is an ERP transition strategy in which the new system and the legacy system operate simultaneously for a defined period, with the same transactions processed in both. Users or finance teams compare outputs, such as ledger balances or order confirmations, to validate that the new ERP produces correct results before the old system is decommissioned. This is the lowest-risk cutover approach because the legacy system remains a live fallback, but it is also the most expensive and labor-intensive, since data must effectively be entered or reconciled twice. Parallel running is most common for finance and payroll, where independent verification of correctness is highly valued. The duration is usually limited to one or a few reporting cycles to control cost.
How Parallel Adoption Works in ERP
In an ERP context, parallel adoption is often applied to a high-stakes area like the general ledger or payroll, where one or two month-end or pay cycles are run in both systems and reconciled line by line. Discrepancies are investigated and traced to configuration, data, or process differences, then corrected. Once the new ERP matches the legacy results to an agreed tolerance, the legacy system is switched off and full reliance shifts to the new platform.
ERP Vendors with Strong Parallel Adoption
SAP S/4HANA Private Cloud
Fully customisable managed-cloud ERP for complex enterprises
Oracle ERP Cloud
Enterprise cloud ERP with deep financials and analytics
Workday
Cloud HCM + financials for services and people-centric orgs
Sage Intacct
Best-in-class cloud financials for services and nonprofits
Frequently Asked Questions
Why is parallel adoption considered the safest cutover method?
Because the legacy system keeps running as a live fallback while the new ERP is validated against it, so if the new system produces wrong results the business is never left without a working system. The safety comes at the cost of double data entry and reconciliation effort.
Why isn't parallel running used for the whole ERP?
Running every process in two systems at once is very expensive and labor-intensive, and some integrated processes are impractical to duplicate. Organizations usually limit parallel running to finance or payroll, where independent verification of correctness justifies the extra effort.