A missed-call calculation can become sales theatre very quickly. Not every caller is a good customer, not every enquiry becomes a quote and revenue is not profit. A useful estimate starts with your own call records and follows each step from unanswered call to completed job.
Build a baseline from a normal month
Count inbound calls, calls answered, calls missed and useful enquiries recovered through voicemail or callbacks. Separate existing customers, suppliers, spam and new opportunities where possible. Four ordinary weeks are more useful than one unusually busy day.
If your phone system does not provide reports, keep a simple tally. The purpose is to establish an honest range, not produce accounting-grade precision.
Estimate the opportunity funnel
Take missed new enquiries and apply three rates: the share you could realistically reach, the share suitable for your business and the share that normally becomes a paid job. Then multiply the resulting jobs by average gross profit, not headline revenue.
For example, ten missed new enquiries are not ten lost jobs. If six are reachable, four are suitable and one usually converts, the monthly opportunity is closer to the gross profit from one job. Use a low and high case so uncertainty stays visible.
Include the cost of interruption
Answering everything has a cost too. Interruptions can slow site work, break a customer conversation and encourage rushed notes that are hard to act on later. Estimate how much working time is lost answering, screening and reconstructing call details.
Do not count every saved minute as cash. Time has value when it reduces overtime, creates quoting capacity or lets the team complete more valuable work.
Compare the complete service cost
Include the subscription, usage allowance, additional call charges, phone number, setup effort, integrations and the time someone spends reviewing summaries. Check what happens if usage increases and whether cancellation or plan changes are straightforward.
An inexpensive service that sends poor messages can cost more than it saves. A higher-priced workflow is not automatically better either. Compare the information and next action produced by real test calls.
Run a measured trial
Record the baseline before switching anything. During the trial, track useful enquiries captured, response time, quotes created, bookings or jobs won, caller complaints and staff time. Keep the same definition of a qualified enquiry throughout.
At the end, ask whether the receptionist recovered opportunities or simply created a new inbox. Continue when the team acts on the information and the value comfortably exceeds the full cost; adjust or stop when it does not.