How accurate is this calculator?

Honest answer: directionally accurate within ~15–25% for the median case in each GMV bracket, less accurate at the extremes. It’s a first-pass screening tool, not a procurement-grade quote.

What it gets right:

• License tier ordering. Magento Open Source $0 vs Adobe Commerce $30k–$150k+ vs SFCC $200k+ — the ranking won’t change.
• Per-tx fee impact at scale. Shopify Plus 0.15% adds up identically every time; the math is exact.
• Dev cost order of magnitude. A $5M GMV store on Magento needs ~$40k upfront + $30k/yr ongoing — the bracket holds across most engagements I’ve seen.

Where it’s less accurate:

• SFCC and Adobe Commerce license — both are negotiated. Tier-1 SI partners often hold ±30% pricing power. The calculator uses public list-equivalent ranges; your actual quote may be lower (negotiated) or higher (uplift for Adobe Commerce Cloud Pro vs Starter).
• Custom dev edge cases — if your scope includes headless commerce, ERP integration, or multi-region inventory orchestration, dev cost can be 2–3x the calculator’s number.
• Region-specific pricing — the model assumes US dev rates. EU SI partners run 0.7–0.9x; India / Eastern Europe freelancers run 0.3–0.5x; Tier-1 US/UK SIs can run 1.2–1.5x.

Use it to rule out platforms and frame the conversation, not to write a budget line.