Upgrading on-premise Dynamics NAV to Business Central without stopping the business

What carries across

Master data, transactional history within the agreed window, and the bulk of standard configuration map cleanly. Business logic that was implemented as configuration rather than code usually survives the move intact.

What gets rebuilt as an extension

Classic C/AL customisations that modified base objects do not move as-is. They are re-implemented as extensions, which is more work up front and dramatically less work at every future update — the object-modification model is exactly what made old NAV upgrades expensive.

• Audit the customisations first; a surprising share are no longer used.
• Re-implement only what the business still relies on.
• Replace bespoke reports with Power BI where it is cheaper.

Phasing the cutover

Cut over at a period boundary, ideally at financial year end, with the legacy system kept readable for the statutory retention period. Run parallel only where the reconciliation actually needs it — full parallel running for months is a cost, not a safety net.

What drives the cost

Number of surviving customisations, integration count, and data volume — in that order. We scope all three before quoting, and we will tell you when the honest answer is to stay on NAV for another year.