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Find the payback month for a launch with a build delay

  • 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 sizing the payback for a new product launch. Write a prompt for plain text with lines starting "Launch cost:", "Contribution starts:", "Months of contribution needed:" and "Payback month:", each with the math. Round the months needed up to a whole month. Payback month counts from the start of the build (month 1). Don't mention the sales team's faster estimate. Under 70 words. No bullets or numbering.

Common mistakes when you ask AI for this

  • Starting the count at month 1. The AI says payback in month 8. Try: Say: "Payback month = build months + months of contribution needed."
  • Not rounding up. The AI shows 7.5 months and month 9.5. Try: Add: "Round months needed up to a whole month."
  • Echoing the sales estimate. The AI says month 6 might be possible. Try: Add: "Do not mention the sales team's estimate or ramp scenarios."
  • 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

  • Names the four lines
  • Gives the rounding
  • Counts the build months
  • Bans the sales estimate
  • Caps length

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