Definition
Cost per call is the total cost of handling a set of calls divided by the number of calls handled. It adds labor, telephony, software and overhead, so the figure depends on which of those a team chooses to include.
How cost per call works
Cost per call = total cost of handling calls / calls handled
The numerator is where teams differ. A full figure has four parts:
- Labor, including wages, benefits, training and supervision, shared across the hours worked and not only the minutes on a call.
- Telephony, such as per-minute carrier charges and phone numbers.
- Software, from the contact center platform to any speech or LLM usage.
- Overhead, such as space, quality assurance and management.
A narrower figure counts only the first two, and a wider one adds all four. Compare only figures built the same way.
For human agents the cost rises with time in the queue as well as time on the call, because staff are paid whether or not the phone rings. For automation the main cost is usually tied to usage, such as minutes of audio processed. The two curves have different shapes. Staffing is a step cost that grows in blocks of people, usage cost grows smoothly with volume. See the AI call center guide for how a total is built up, and Twilio pricing for the telephony piece.
Why it matters for voice agents
The risk is dividing by the wrong number. A call the agent fumbles and then transfers costs the automated minutes and the human minutes. If those calls are counted as one automated call and one human call, the average looks better than it is. A fairer figure is cost per resolved call: total spend on automation and on the humans who picked up its transfers, divided by calls that were actually resolved.
Cost also follows average handle time, because usage-based charges scale with duration. A longer call that avoids a repeat call can still be the cheaper path. For Cartesia plans and prices, see the pricing page.
Example
An illustrative month (invented numbers): total spend of $12,000 across automation and the staff handling its transfers, 2,000 calls handled, 1,600 of them resolved.
Cost per call is $6.00. Cost per resolved call is $12,000 / 1,600 = $7.50.