The ROI calculations in vendor sales decks are useless. They're built on industry averages, inflated time estimates, and assumptions about your cost base that have nothing to do with your actual business. Here's a framework you can run yourself, using numbers you already have.

Step 1: Quantify the current cost of the process

Pick one specific process — not a department, a single repeatable task. For each person involved, calculate:

  • How many hours per week do they spend on this task?
  • What is their fully-loaded hourly cost (salary + overhead, typically 1.3–1.5x base salary)?

Multiply those two numbers and annualise. This is your labour cost baseline. Add any direct costs: software licences used only for this process, external services, error-related costs (rework, disputes, delays).

Step 2: Estimate the automation coverage rate

Not every instance of a process can be automated. Most document-processing tasks achieve 85–95% coverage — meaning 5–15% still require human review. Estimate honestly. The safest approach is to assume the lower end of coverage during planning and treat anything above that as upside.

Your automated volume = (total annual instances) x (coverage rate). Your residual manual volume = what's left.

Step 3: Calculate residual labour cost

The residual manual work (the uncovered 5–15%) still costs time. Estimate the time per instance for human review of AI-flagged exceptions — this is usually 20–40% of the original time per instance, since the AI has already done the initial processing.

Residual labour cost = (residual instances) x (review time per instance) x (hourly cost)

Step 4: Estimate implementation and running costs

These vary widely by complexity. As rough planning figures:

  • Simple document automation (one document type, one output format): 30–60k EUR implementation
  • Multi-document, multi-system integration: 60–120k EUR
  • AI agent with complex business logic: 80–180k EUR
  • Annual running costs (hosting, maintenance, model updates): 10–20% of implementation cost

Get a real quote before using these numbers for any decision. They exist only to give you a planning range.

Step 5: Calculate payback period

Annual saving = (current labour cost) + (current error costs) - (residual labour cost) - (annual running cost)

Payback period = implementation cost / annual saving

If the payback period is under 18 months for an SMB or under 24 months for an enterprise, the project is worth scoping in detail. If it's over 36 months, the numbers don't support it at current pricing.

A note on what this doesn't capture

This framework only captures direct labour cost savings. It doesn't account for speed improvements (faster processing enables faster billing cycles, shorter cash conversion), error reduction (fewer supplier disputes, fewer customer complaints), or team capacity reallocation. Those are real but harder to quantify at the planning stage. Treat them as secondary justification, not primary.

The strongest business cases are built on conservative labour cost estimates and realistic coverage rates — not the optimistic version of both.