Calculate incremental contribution from completed work, not the face value of bookings. Include jobs your existing callback process would already have recovered, and cap the upside at work your engineers can actually deliver.
A practical calculation
For a comparable group of eligible enquiries:
Incremental completed jobs = eligible enquiries × (pilot completion rate − baseline completion rate)
For a positive scenario, cap that result at additional deliverable capacity.
Monthly net contribution = incremental completed jobs × contribution per job − all incremental recurring costs
First-year net benefit = sum of monthly net contributions − setup and transition costs
Use contribution after the variable costs of delivering the additional job. Agree the definition with finance; do not mix turnover, gross margin and cash receipts.
Hypothetical worked example—not an HVAC benchmark
| Assumption | Illustration |
|---|---|
| Eligible enquiries in the comparison group | 60/month |
| Baseline completed-job rate, including callbacks | 20% |
| Pilot completed-job rate | 35% |
| Calculated additional jobs | 9/month |
| Additional delivery capacity | 8/month |
| Contribution per additional completed job | £150 |
| Total recurring cost, including supervision | £650/month |
| Setup and transition | £3,000 |
The capacity-limited illustration produces £1,200 contribution less £650 recurring cost: £550/month. Twelve identical months less setup would produce £3,600, but only if those assumptions held.
At four extra jobs, the same arrangement loses £50/month before setup. Recurring break-even requires five whole jobs; spreading setup evenly over the first year raises the illustrative requirement to six.
Report released office time separately. Count it as cash saving only when expenditure actually falls, or as additional contribution only when the resulting extra output is demonstrated. Do not count the same benefit twice.