Net benefit and payback period of deploying AI to replace labour hours

Why AI ROI Calculations Miss the Point

Most AI ROI calculations stop at the subscription cost of the tool. 20/month for ChatGPT Plus versus 100/month saved on a freelancer equals simple win. The bigger picture is different. Real AI implementation in a business has four cost layers: upfront tool selection and setup, ongoing subscription fees, training and workflow redesign time, and the opportunity cost of work that breaks because AI produces subtly wrong output that nobody catches. This calculator models the first two and the time-saving benefit; the third and fourth need judgement beyond a spreadsheet.

The Time-Saving Multiplier

AI productivity savings follow a power-law distribution. Tasks that are genuinely suited — drafting content, summarising documents, generating code boilerplate, first-pass image generation — can save 70-90% of the time. Tasks that require human judgement or deep context — strategic decisions, nuanced client communication, novel problem-solving — save 10-30% at best. Mixed tasks land in the middle. The tool assumes a flat hours-saved-per-week figure. Run it separately for each workflow rather than averaging across everything.

Realistic Hours-Saved Benchmarks

Marketing content drafting (blog posts, emails, ad copy): 5-15 hours/week/person saved at moderate quality, higher with heavy editing. Customer support (first-line FAQ handling, ticket triage): 10-30 hours/week saved for teams of 3+. Software engineering (boilerplate, docstrings, test scaffolds, bug explanations): 5-10 hours/week/engineer. Data analysis (SQL generation, chart explanation, summary reports): 3-8 hours/week. Translation and localisation: 50-80% time savings. Design (initial mockups, style variations): 20-40% savings but human finishing still needed.

The Hourly Rate Gotcha

Use fully-loaded cost, not payroll. A 60/hour engineer costs the company closer to 90-120/hour after benefits, equipment, facilities, management overhead, and non-billable time. If you use just payroll, ROI understates the real benefit by 30-50%. Same applies to outsourced labour — use total landed cost including project management oversight, not just the contractor's rate. For consultants, include the full day rate.

Worked Example

Marketing team of 4 adopts an AI writing tool. Implementation cost: 5,000 (tool selection, initial integration, team training). Annual ongoing cost: 3,600 (75/month/user × 4 users × 12). Hours saved per week: 25 hours/week across the team. Fully-loaded hourly cost: 85. Analysis horizon: 3 years. Annual benefit: (25 × 48 × 85) - 3,600 = 98,400. 3-year net benefit: (98,400 × 3) - 5,000 = 290,200. ROI: 5,804%. Payback period: ~19 days of annualised savings. At this scale, AI adoption is a clear win even with 50% haircut for overstated savings.

When ROI Goes Negative

Implementation cost too high relative to savings (enterprise tool for a 2-person team). Time savings overestimated (using 20 hours/week when reality is 5). Ongoing cost scales with usage (per-API-call pricing on low-margin work). Hidden quality costs (AI output needs heavy human review, eroding the time-save advantage). Change management costs (team resistance, workflow redesign, retraining). The calculator flags payback over the horizon as negative ROI — if that is the result, either scale the deployment smaller, pick a cheaper tool, or defer adoption until the use case is clearer. Another common failure mode: positive calculated ROI but no organisational capacity to actually capture the savings. Saving 20 hours a week means those hours need to be redeployed to higher-value work. If the team just fills the newly-free time with more low-value activity, the financial benefit evaporates even though the tool works.