Review a representative period of calls. Separate missed new enquiries from repeat calls, spam and existing-customer questions. Note when they happen and whether your team has time to respond.
If there are few missed enquiries and your current process works, another service may add cost without much benefit. If calls repeatedly interrupt paid work or disappear into an unattended inbox, a measured trial is more useful than a headline return-on-investment claim.
For a simple sales-only check, divide the total monthly service cost by the contribution from one additional completed job. Contribution means the money left from that job after its direct variable costs, not the full invoice value. This adapts the basic break-even approach explained by the U.S. Small Business Administration.
Illustration only: if the full incremental monthly cost is $200 and an additional completed job contributes $100 after direct costs, two extra jobs cover that cost. Three contribute $100 beyond it, before any additional overhead. Use your own figures and include the service’s usage and follow-up costs.
Only count work that would otherwise have been lost. If the customer would have booked anyway, it is not additional revenue created by the answering service.
Useful enquiries: how many contained the correct contact details and enough context for your team to act?
Completed outcomes: how many led to a genuine next step, such as a completed job or confirmed appointment?
Time saved: how much interruption or administration was removed, after allowing for review and corrections?
Customer experience: did callers get correct answers and a realistic expectation of the next step?
Full cost: plan and usage charges, connected services, plus the time your team spends following up.
Choose one defined use case, such as missed new-business calls. Keep a comparable record of your current process.
Agree the information to collect and name the person responsible for follow-up. An unworked enquiry is not a completed result.
Test routine calls and exceptions, then review a manageable set of real enquiries using appropriate privacy controls.
Compare costs and completed outcomes. Keep time savings separate from cash revenue so you do not count the same benefit twice.
Continue, adjust or stop based on what you observed. Avoid projecting a few unusually valuable calls as a guaranteed monthly return.