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Compute CAC, payback and LTV:CAC after a cost correction
- For FP&A and financial analysts
- You practice Catching mistakes and made-up facts
- Time about 5 minutes
- Level Intermediate
About this exercise
You're preparing a unit-economics note for the CFO. Write a prompt for plain text with exactly four lines, no intro, starting "CAC:", "Payback:", "LTV:" and "LTV:CAC:", each showing the arithmetic. Use only sales and marketing spend after the controller's reclass. Give figures only and make no recommendation about spending. Under 75 words. No bullets or numbering.
Common mistakes when you ask AI for this
- Using the GL spend. The AI divides $540,000 by 60 for a $9,000 CAC. Try: Say: "Remove the $60,000 reclass before dividing."
- Payback on revenue, not margin. The AI divides CAC by $500, not $400. Try: Add: "Gross profit per month = ARPA x gross margin."
- Recommending spend. The AI answers the board member's question about doubling marketing. Try: Add: "Figures only. No recommendation about spending."
- Markdown extras. The AI adds bold labels, headings and a closing note. Try: Say: "Plain text, no bold. Output only the lines asked for."
- Trusting the AI to count words. AI is bad at counting and runs past word limits. Try: Ask for fewer words than the real cap and keep each line short.
What a strong prompt includes
- Lists the four lines
- Applies the reclass
- Uses given formulas
- Bans recommendations
- Caps length
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