# How to Track Voice AI Agent ROI (With Formulas)

Build a voice AI ROI dashboard in Google Sheets. Four metrics that matter, the exact formulas, and a worked example from a plumbing company making 642x return.

From the book: [How to Build Voice AI Agents](https://youcanbuildthings.com/books/voice-ai-agents.md)

Web page: https://youcanbuildthings.com/articles/voice-ai-agent-roi-calculator

> **Summary:**
> 1. One formula tells you if your voice AI agent is worth keeping.
> 2. A 5-minute Friday routine that tracks everything you need.
> 3. Worked example: a plumbing company paying $171/month, booking 312 appointments.
> 4. What to fix when the numbers don't look right.

Three weeks into running his voice AI agent, a plumber in Phoenix told me: "I think it's working. I'm getting more calls." How many more? "I don't know. More." What's it costing? "I don't know. Less than the answering service?"

"Probably" doesn't justify a monthly expense. One formula does.

## Is it worth it? One formula, 30 seconds.

If you hate spreadsheets, ignore everything else in this article except this:

```
Agent cost this month:    $______
Appointments it booked:   ______
Cost per booking:         $______ (cost / appointments)
Your average job value:   $______
```

**The rule:** if the cost per booking is less than 10% of your average job value, keep the agent. If it's more, fix the prompt before blaming the platform.

Martinez Plumbing (reported numbers): $171 / 312 appointments = **$0.55 per booked appointment.** Average job: $380. The agent cost less than a penny for every dollar it generated. He stopped saying "I think it's working."

That's the whole decision. If you want more detail, keep reading.

## How does your agent compare to what you had before?

This is the table you show your business partner or your accountant. Fill in both columns with your actual numbers:

| Metric | Before Agent | With Agent |
|--------|-------------|------------|
| Monthly phone cost | $______ | $______ |
| Calls answered/month | ______ | ______ |
| Appointments booked/month | ______ | ______ |
| Cost per call | $______ | $______ |

For reference, here's what Martinez Plumbing reported after switching:

| Metric | Before (answering svc) | With Agent | Change |
|--------|----------------------|------------|--------|
| Monthly phone cost | $650 | $171 | -74% |
| Calls answered | 800 | 1,247 | +56% |
| Appointments booked | 195 | 312 | +60% |
| Cost per call | $0.81 | $0.14 | -83% |

These are reported numbers from one business. Your results will depend on your call volume and average job value. He cancelled the answering service the day he filled this in.

![Voice AI ROI dashboard showing cost per call, lead capture rate, booking rate, and 642x ROI with Google Sheets formulas and cost comparison](https://youcanbuildthings.com/images/articles/voice-ai-agent-roi-calculator/roi-dashboard.jpg)

## How do you track this every week? (5 minutes, every Friday)

Open a Google Sheet. One row per week. These columns:

```
Week Starting | Total Calls | Appointments Booked | Platform Cost | Revenue
```

Every Friday, fill in one row. Takes 5 minutes:
- **Total Calls:** from your Bland dashboard
- **Appointments Booked:** count agent-created calendar events
- **Platform Cost:** your weekly pro-rated fee (~$47/week at $200/month)
- **Revenue:** total from this week's agent-booked jobs

Two formulas in the next column:

```
Cost per booking:  = Platform Cost / Appointments Booked
Weekly ROI:        = Revenue / Platform Cost
```

That's the whole system. After four Fridays you'll see the trend. If it's climbing, the prompt is getting better. If it's falling, read the troubleshooting section below.


## What do you do when the numbers don't look right?

Four scenarios and their fixes.

**Booking rate under 20%.** The agent answers calls but doesn't convert them to appointments. Pull up 5 recent non-booking transcripts in your Bland dashboard. Find the moment where the caller could have been offered an appointment but wasn't. Add to the prompt: "After answering a pricing or availability question, always ask: 'Would you like to go ahead and schedule?'"

**Too many calls going to a human (over 25% transfer rate).** Review what triggers the transfers. Usually it's questions the agent can't answer. Add those Q&As to the prompt. One Friday of transcript reading fixes most transfer leaks.

**Calls running too long (average over 4 minutes).** The agent is rambling or stuck in loops. Add to the prompt: "Keep responses to 2-3 sentences. If the question is answered, ask if they need anything else and wrap up."

**Revenue doesn't justify the cost after 4 weeks.** Either the prompt isn't converting (fix it) or your call volume is too low. Below 10 calls a day, a $200/month agent might not pencil out. Try after-hours only or a pay-per-call plan.

Every ROI calculator on Google's first page for "voice AI agent ROI" is a lead-gen form from companies like [CloudTalk](https://www.cloudtalk.io/ai-voice-agent-roi-calculator) and [VoiceInfra](https://voiceinfra.ai). They want your email. This worksheet gives you the same answer without the sales call.

## What should you actually do?

- If you haven't tracked anything yet: fill in the one-formula box at the top of this article. Takes 30 seconds.
- If that looks good and you want ongoing proof: start the Friday spreadsheet. One row per week, 5 minutes.
- If the numbers look off: read 5 call transcripts. The fix is almost always in the prompt, not the platform.

## bottom_line

- One formula: agent cost divided by booked appointments. If that number is under $5 and your average job is $300+, the agent is working. Stop overthinking it.
- Five minutes every Friday is the whole tracking system. One row, two formulas, done.
- When the numbers don't work, fix the prompt first. Nine times out of ten, the platform is fine and the prompt is the bottleneck.

## FAQ

### How much does a voice AI agent cost per month?

Most small businesses pay $150-400/month depending on call volume. Bland.ai charges about $0.09/min with no subscription. A business handling 50 calls/day at 2 minutes each pays roughly $270/month. Add $9/month for Make.com integrations.

### How long does it take to see ROI from a voice AI agent?

Most businesses see positive ROI within the first week. The agent costs $5-10/day to run. If it books even one appointment that voicemail would have missed, it's paid for itself.

### What's a good booking rate for a voice AI agent?

25-40% is typical and comparable to a human receptionist. Below 20% means your prompt needs better conversion triggers. Add 'After answering a pricing question, always ask: Would you like to go ahead and schedule?' to your prompt.

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Get the book: How to Build Voice AI Agents, $9.99 on Amazon: https://amzn.to/4161PAx