Legacy ERP Parallel Run Cost Calculator
A parallel run feels safe, but it keeps two systems alive and doubles some work. This calculator prices that safety so you can choose the shortest run that still protects you.
Your numbers
Licences, hosting, support and admin that continue during the overlap.
Your results
Planning estimate. Replace defaults with your contract and payroll figures.
Extra cost vs parallel months
Sweeps Parallel run length from 1 to 12, holding your other inputs fixed.
Optional reconciliation automation
Ask how automated legacy to new comparisons could shorten your overlap.
Optional. The tool and every export work without this. No spam.
How to use it
Enter the legacy cost that cannot be cancelled during the overlap, such as licence terms, hosting and support. Add double entry only if users truly key transactions twice. If you load data nightly instead, set the staff to zero and put the checking time into reconciliation hours.
The method
Incremental monthly cost equals legacy monthly cost plus extra labour. The new system cost is not incremental because it is spent regardless, though the tool shows total spend for reference. Total extra cost is incremental monthly cost times months, and the weekly figure shows what each slipped week costs.
Choosing a length
Most teams need at least one full period close, often two. Parallel running past a clean quarter-end rarely adds assurance. Use the chart to see how the cost climbs per month and set an exit criterion such as three consecutive reconciled closes, rather than a calendar date alone.
- Define exit criteria first
- Cancel what you can early
- Negotiate short legacy extensions
- Automate reconciliation
Frequently Asked Questions
Is a parallel run mandatory?
No. Some companies cut over after rehearsals and keep the legacy system read-only. A parallel run suits high-risk financial processes, but it costs time and attention that rehearsals can often replace.
Why exclude the new system cost?
Because you will pay it whether or not you run in parallel. Only costs that exist because of the overlap belong in the incremental figure.
What does reconciliation cover?
Comparing trial balance, open AR and AP, inventory valuation and key reports between systems, and investigating differences.
How long should the legacy system stay readable?
Often for audit and tax retention periods, typically several years. See the data growth and archive calculator for storage planning.
Netray can build automated reconciliation between legacy and new ERP data so the run can be shorter. The calculator is independent of that.
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