Freeze the comparison inputs
Use the same employee population, attendance results, salary structures and approved adjustments in both runs. Record the version of each input. If a correction arrives halfway through testing, apply it consistently or exclude it from the comparison with a clear explanation.
Compare at component level
Review employee count, individual earnings, deductions and net pay. Check rounding and effective dates before assuming a rule is incorrect. Include edge cases such as a partial period or a revision; a test made entirely of unchanged full-month records gives limited confidence.
Set an explicit acceptance decision
Record every unresolved difference and assign an owner. The decision to proceed should be based on understood outcomes and approved configuration. Keep evidence of the accepted run so future reviewers know what was tested and which limitations remained.
Worked example
Both systems produce the same overall total, but one employee's allowance and another employee's deduction differ. Component-level reconciliation exposes the offsetting differences that a total-only check misses.
Practical checklist
- Use identical input versions.
- Test representative exceptions, not only normal records.
- Document acceptance and unresolved items.