Planning Parallel Run Periods to Validate New ERP System Functionality

What Is a Parallel Run Period in ERP Migration?

A parallel run period is a critical validation phase where both the legacy ERP system and the new target ERP system operate simultaneously for a defined duration. During this time, identical business transactions are processed in both environments to verify that the new system produces accurate, consistent, and compliant results. This approach is essential for high-risk migrations, particularly those involving financial modules, complex supply chain logic, or significant customizations. The primary goal is to reduce the risk of data loss, financial misstatement, and operational disruption by providing a safety net before the legacy system is decommissioned. Key risks to control include data reconciliation errors, performance degradation under load, integration failures, and user confusion due to dual-entry requirements. A well-planned parallel run requires strict governance, clear success criteria, and a defined exit strategy to ensure the transition is both safe and timely.

Defining the Scope and Objectives of the Parallel Run

Before initiating the parallel run, stakeholders must define the scope to avoid resource exhaustion and ambiguity. Determine which modules will be included in the parallel run. Typically, core financials (General Ledger, Accounts Payable, Accounts Receivable) and inventory management are mandatory. Other modules like HR or CRM may be excluded if their data dependencies are lower or if they can be migrated in a subsequent phase. The objective is not to replicate every single transaction if the volume is unmanageable, but to cover representative business cycles. For example, if the company operates on a monthly close cycle, the parallel run should cover at least one full monthly close, including accruals, reconciliations, and reporting. Define the specific business processes to be validated, such as order-to-cash, procure-to-pay, and record-to-report. This scope definition ensures that the team focuses on high-value validation activities rather than getting bogged down in low-impact data points.

Selecting Representative Data Sets

The validity of the parallel run depends on the quality and representativeness of the data used. Do not use sanitized or dummy data for the final parallel run; use a production-like snapshot of the legacy system. This snapshot should include master data (customers, vendors, items) and transactional data from the period immediately preceding the run. Ensure that the data mapping rules have been tested and approved. If the new ERP uses different chart of accounts structures or item hierarchies, the transformation logic must be verified. The data set should include edge cases, such as multi-currency transactions, intercompany entries, and complex tax scenarios. By using realistic data, you can identify gaps in the migration logic that synthetic data might miss. This step is crucial for ensuring that the new system can handle the actual complexity of the business.

Establishing Data Reconciliation Protocols

Data reconciliation is the core activity of the parallel run. It involves comparing the outputs of the legacy and new systems to identify discrepancies. Establish a clear protocol for how data will be compared. This typically involves generating trial balances, sub-ledger balances, and key performance indicators from both systems. Define the tolerance levels for variances. For financial data, even small variances can be significant, so a zero-tolerance policy may be required for certain accounts. For operational data, such as inventory counts, a small percentage variance might be acceptable if it is within statistical norms. Create automated reconciliation scripts where possible to reduce manual effort and human error. These scripts should flag discrepancies for investigation. Assign specific owners to each reconciliation area, such as the Finance Manager for GL reconciliation and the Supply Chain Manager for inventory reconciliation. This ownership ensures that discrepancies are resolved promptly and systematically.

Managing Operational Workflows and User Roles

During the parallel run, users must enter data into both systems or have data synchronized automatically. Manual dual-entry is labor-intensive and prone to errors, so it should be avoided if possible. If manual entry is required, provide clear instructions and training to users. Define which users will be involved in the parallel run. Ideally, a subset of key users from each department should participate to ensure that the system is tested by those who understand the business processes. These users should be available to report issues and provide feedback. Establish a communication channel for reporting discrepancies. This could be a dedicated email address, a ticketing system, or a daily stand-up meeting. Ensure that all issues are logged, tracked, and resolved in a timely manner. The goal is to maintain operational continuity while validating the new system. Users should not be expected to stop their regular work to perform parallel run tasks; instead, the parallel run should be integrated into their daily workflow as much as possible.

Handling Discrepancies and Defects