The allowable-CPL math

The most you can pay for a booked call

It works backwards from what a customer is worth to the most you can pay per customer, per showed call, per booked call and per lead. It shows every step, gives worst and best cases, and writes down what "working" means before you spend.

Work it out

The numbers below are an EXAMPLE, not anyone’s results. Replace them with yours.

Revenue from one new customer$Gross margin%Share of gross profit you’ll spend to win a customer%Close rate (of showed calls)%Show rate (of booked calls)%Booking rate (of leads)%

Per customer: $1,500
Per showed call: $375
Per booked call: $300
Per lead: $90

Each number multiplies the one before it by a rate. If one comes out bigger than the one above it, a rate is above 100%.

The prompt: paste it into ChatGPT or Claude and fill in the blanks

Prompt

Work out the most I can pay for a customer, a showed call, a booked call and a
lead. Show every step. Multiply by the rates. Never divide by them.

My numbers (I've written ESTIMATE next to any I'm guessing):
- Revenue from one new customer: [$]
- Gross margin (the share left after delivery costs): [%]
- Share of that gross profit I'm willing to spend to win one customer:
  [%; a third is a common starting point]
- Close rate (showed calls that become customers): [%]
- Show rate (booked calls that actually happen): [%]
- Booking rate (leads that book a call): [%]

Steps:
1. Allowable cost per customer = revenue x gross margin x share.
2. Allowable cost per showed call = step 1 x close rate.
3. Allowable cost per booked call = step 2 x show rate.
4. Allowable cost per lead = step 3 x booking rate.

Then give a worst, expected and best case by moving each rate I marked ESTIMATE
down and up by a quarter of its value.

Then write two sentences: what "working" means (a cost per booked call at or
under step 3, at a stated number of leads a week, by a stated day) and what
"kill it" means.

If the allowable cost per lead is lower than my market can plausibly deliver,
say so plainly: that is an offer or sales problem, not an ad problem.

How to use it

What it does. It works backwards from what a customer is worth to the most you can pay per customer, per showed call, per booked call and per lead. It shows every step, gives worst and best cases, and writes down what "working" means before you spend.

When to use it. Before the first ad. It sets your budget, your kill rule and your scale ceiling.

What a good output looks like. Four numbers, each smaller than the one before, with the arithmetic shown. A worst, expected and best table. Two plain sentences.

EXAMPLE, to check the AI's arithmetic. These are not anyone's numbers:

Step	Arithmetic	Result
Per customer	$9,000 × 50% × one third	$1,500
Per showed call	$1,500 × 25% close rate	$375
Per booked call	$375 × 80% show rate	$300
Per lead	$300 × 30% booking rate	$90

Check it. If any number is bigger than the one above it, the AI divided. Run it again.

Get it as a file

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Every prompt behind the lead system