How to Estimate Cloud Migration Cost (Without Surprises)

Most cloud-migration budgets miss not because the obvious costs are wrong, but because the hidden ones were never counted: data egress, running old and new in parallel during cutover, new platform licences, and post-migration right-sizing. A defensible estimate isn't a single number someone hands you — it's a short method you can run yourself. Here's the one we use. (For the bigger picture of what drives cost, see cloud migration services: planning, process & cost.)

List every app, server, database, and dependency. Tag each as move, retire, or stay. The cheapest workload to migrate is the one you switch off — most estimates shrink the moment you cut what's unused. You can't price a migration you haven't inventoried.

Apply the 6 R's per item — rehost, replatform, refactor, repurchase, retire, retain. Rehosting is cheapest to execute; refactoring costs more up front but lowers run-cost. Your estimate is the sum of per-workload choices, not one blanket approach.

Data is where timelines and bills surprise people. Estimate volume, change rate, and coupling. Large or tightly-coupled data takes longer, may need a dedicated transfer approach, and incurs egress charges. Factor the transfer window into downtime planning too.

Budget explicitly for: dual-running (old + new in parallel during cutover), egress fees, new licences on the target platform, migration tooling, and post-migration right-sizing. These are the items that turn a "fixed" quote into a true-up. Naming them up front is how you avoid the surprise.

The project cost is one-off; the cost that decides ROI is what you pay to run the result. Estimate monthly compute, storage, and support for the target state, then compare three-year totals against today. A migration that costs more to do but lowers run-cost and outage risk is usually the better buy. Put your numbers into the ROI & TCO calculator to see the comparison.

This method gets you a defensible range; the exact figure needs a scope of your environment. Book a free consultation and we'll turn your inventory into a transparent, waved plan with rollback criteria — no surprise true-ups.