How to Calculate Pay-Per-Call ROI (With Two Worked Examples)

What numbers do you need before you start?

Pay-per-call ROI comes down to five inputs. Estimate the ones you do not know, then replace them with real data after your first month. If you do not know your close rate, do not guess high: pull your last 50 to 100 inbound inquiries and count how many became jobs.

• Billable calls per month: calls you actually pay for, after credits for calls that do not qualify
• Close rate: the share of billable calls that become paying customers (for a law firm, signed cases)
• Average job value: what a typical new customer pays for the first job or case
• Gross margin: the share of that revenue left after labor, materials, subcontractors, or case expenses
• Cost per call: the price of each billable call

How do calls turn into customers and revenue?

The core chain is short. Calls x Close rate = New customers. New customers x Average job value = Revenue. Revenue x Gross margin = Gross profit. Gross profit minus Call spend = Net contribution from the channel.

Why should you use gross profit instead of revenue?

Revenue is not what you keep. A plumber who bills $800 for a water heater swap pays for the heater, the truck, and the technician's hours first. A law firm that collects a $15,000 fee has paid for filing fees, records, experts, and attorney time along the way. Compared against revenue, pay-per-call looks better than it is. Compared against gross profit per job, you get the honest picture.

How do you calculate CAC and break-even close rate?

Customer acquisition cost (CAC) is total call spend divided by the number of new customers those calls produced. If you spent $4,000 on calls and closed 14 jobs, your CAC is $285.71 per job.

Break-even close rate answers a different question: how many calls do you need to close for the channel to pay for itself on the first job alone? The formula is cost per call divided by gross profit per job. At $100 per call and $400 gross profit per job, break-even is 25 percent. Close one in four and you are at zero. Close better than that and every extra job is profit.

What is the most you should pay per call?

Flip the break-even formula around. Maximum affordable cost per call equals your close rate times your gross profit per job. If you close 35 percent of calls and earn $400 gross profit per job, you can pay up to $140 per call and still break even on the first job. When a provider quotes a price for your vertical and territory, compare it against this ceiling instead of reacting to whether it sounds expensive.

Worked example: what does the math look like for a plumber at $100 per call?

Assume a residential plumber pays $100 per billable call and receives 40 billable calls in a month, for $4,000 in spend. The plumber closes 35 percent of calls, the average first job is $800, and gross margin after labor and materials is 50 percent, so each job produces $400 in gross profit. These are illustrative figures; replace them with your own.

• New customers: 40 x 0.35 = 14 jobs
• Revenue: 14 x $800 = $11,200
• Gross profit: $11,200 x 0.50 = $5,600
• Net contribution: $5,600 minus $4,000 = $1,600
• CAC: $4,000 / 14 = $285.71 per job
• Break-even close rate: $100 / $400 = 25 percent
• Maximum affordable cost per call at a 35 percent close rate: 0.35 x $400 = $140

The plumber is profitable on first jobs alone, with about $1,600 left after paying for the calls. That margin is not enormous, which is the honest point: the channel works when phones are answered and the close rate holds. Drop to 25 percent and it only breaks even. Repeat work and referrals from those 14 households are upside on top.

Worked example: what does the math look like for a personal injury firm at $1,000 per call?

Now assume a personal injury firm pays $1,000 per billable call and receives 30 billable calls in a month, for $30,000 in spend. Many callers have no viable case, so the firm signs 4 of the 30, about 13 percent. Assume the average signed case eventually produces a $15,000 fee and gross margin after case costs and attorney time is 60 percent, so each signed case produces $9,000 in gross profit.

• Signed cases: 30 x 0.133 = 4 cases
• Fee revenue: 4 x $15,000 = $60,000
• Gross profit: $60,000 x 0.60 = $36,000
• Net contribution: $36,000 minus $30,000 = $6,000
• CAC: $30,000 / 4 = $7,500 per signed case
• Break-even sign rate: $1,000 / $9,000 = 11.1 percent
• Maximum affordable cost per call at a 13.3 percent sign rate: 0.133 x $9,000 = about $1,200

The firm is profitable, but look at how close the sign rate sits to break-even. Signing 3 cases instead of 4 flips the month to a loss. That is normal for high-ticket verticals: small changes in intake quality swing the result, which is why intake training matters as much as the calls themselves.

One more difference: the plumber gets paid this month. The law firm may wait a year or more for the fee, so ROI can be positive while cash flow is negative for a long stretch. A firm needs the reserves to carry the spend.

What does this math leave out?

The first-job model is deliberately conservative. It leaves out:

• Repeat business and referrals: count these as upside, not as a reason to pay more up front
• Credits: where calls that do not qualify are credited, use billable calls in the math, not raw calls
• Time cost: someone has to answer the phone and run the estimate or intake, so include that labor in gross margin
• Answer rate: a call you miss during posted hours may still be billed, which raises your effective cost per answered call

How should you use these numbers?

Run the math with your own figures before you buy calls anywhere, from anyone. Set your break-even close rate and maximum cost per call. Run a first month, replace the estimates with real numbers from your call log, and recalculate. If the channel clears break-even with room to spare, scale it. If not, the data will usually show whether the problem is call quality, close rate, or price, and those have different fixes. Per-call pricing with no monthly fee makes the test cheap to run, but the math is the same for any lead source.