Pull the call log
Your phone provider has a log of every inbound call with duration. Calls under ten seconds with no answer are the missed ones. Count them for one normal week, by hour.
Count the after-hours share
Sort by time. Most offices find a third of missed calls between 5 pm and 9 am, and a quarter on Saturday.
Estimate the booking rate
Of the calls you do answer, what share becomes a booking or a job? Use that rate on the missed ones. Be conservative and take half.
Value per booking
Average ticket for a first visit or a first job. For a salon that is often $80 to $200, for a shop $300 to $600, for a clinic the first visit value, for a carrier the average load.
The number
Missed calls a week, times the booking rate, times the value, times four. That is the monthly cost. Run it in the calculator on this site and keep the page.
Then decide
If the number is under the monthly fee, do nothing yet. If it is three times the fee, you already know.