HomeCasa Unit economics check: contribution margin, CAC, LTV and payback
Find out whether each customer makes or loses you money: calculate contribution margin, CAC, LTV, LTV:CAC ratio and payback months, with a sensitivity analysis. Designed for ChatGPT, Claude, Gemini and Microsoft Copilot. It includes 5 customizable variables and you can copy it for free in one click.
Advanced · Text · Pending editorial review
Prompt
Act as a financial analyst who specializes in startups and digital businesses. Review my unit economics step by step, showing every calculation.
Data:
- Business model: {{model}}
- Average revenue per customer or per order: {{revenue}}
- Variable costs per customer or order (product, shipping, fees, support): {{variable_costs}}
- Acquisition: sales and marketing spend and new customers in the same period: {{acquisition}}
- Retention: monthly churn or repeat purchase rate: {{retention}}
Before calculating, summarize the inputs in a table and ask me about anything missing or ambiguous (for example, whether revenue includes sales tax or whether acquisition spend includes salaries).
Deliverables:
1. Contribution margin per order or per customer per month, in dollars and as a percentage.
2. Blended CAC (total spend ÷ all new customers) and, if data allows, paid-only CAC.
3. LTV based on margin (not revenue), with the formula shown. Give a conservative and a base scenario.
4. LTV:CAC ratio and CAC payback period in months.
5. A sensitivity table: what happens if CAC rises 20%, churn rises 2 points or price rises 10%.
6. Diagnosis: healthy, warning or broken, with reasons. If you compare against common rules of thumb (such as 3:1 LTV:CAC), say they are rough guides, not laws.
7. The 3 highest-impact levers, ranked, with one concrete action to test for each.
8. The metrics I should track monthly and where to get them.
Constraints:
- Show all formulas and arithmetic. Do not invent data: if something is missing, use [FILL IN] and explain how to get it.
- This is not financial advice; recommend validating the figures with an accountant or advisor.
Format: tables for inputs and calculations, bullet points for the diagnosis.How to use it
- Pull the last 3-6 months of data from your accounting, store or CRM. 2. Use the same period for acquisition spend and new customers. 3. Repeat the check every quarter to see the trend.
Usage example
Model: natural skincare e-commerce · Average order: $42 · Variable costs: $19 · Acquisition: $4,500 and 150 new customers in a quarter · Repeat: 30% reorder within 6 months.
Sample output
Inputs
| Input | Value |
|---|---|
| Revenue per customer | $29/month |
| Variable costs | $7/month |
| Acquisition spend | $6,500 over 3 months |
| New customers | 120 |
| Monthly churn | 5% |
Question first: does the $29 include sales tax? Does the $6,500 include salaries? I assume no to both.
Calculations
| Metric | Formula | Result |
|---|---|---|
| Contribution margin | 29 − 7 | $22/month (75.9%) |
| Blended CAC | 6,500 ÷ 120 | $54.17 |
| LTV, base | 22 ÷ 0.05 | $440 |
| LTV, conservative (7% churn) | 22 ÷ 0.07 | $314.29 |
| LTV:CAC | 440 ÷ 54.17 | 8.1 : 1 (5.8 conservative) |
| CAC payback | 54.17 ÷ 22 | 2.5 months |
Sensitivity
- CAC +20% ($65.00): LTV:CAC = 6.8; payback 3.0 months.
- Churn +2 points (7%): LTV:CAC = 5.8.
- Price +10% ($31.90): margin $24.90; LTV = $498; LTV:CAC = 9.2.
Diagnosis: healthy, with caveats
- Well above the 3:1 rule of thumb, which is a rough guide, not a law.
- With only 3 months of data, churn may not have stabilized yet: [FILL IN: churn by cohort].
Validate these figures with an accountant or advisor…
Key facts
- Category
- Business & entrepreneurship · Business models
- Output type
- Text
- Level
- Advanced
- Designed for
- ChatGPT, Claude, Gemini and Microsoft Copilot
- Verified in
- Pending editorial verification
- Variables
- Business model, Average revenue per customer or order, Variable costs, Acquisition spend and new customers and Retention
- Language
- English
- Price
- Free, no sign-up
- Updated
- Nov 7, 2026
Frequently asked questions
Why calculate LTV from margin instead of revenue?
Because acquisition is paid for by what is left after variable costs. Revenue-based LTV inflates customer value and can make a money-losing business look profitable.
What is a good CAC payback period?
It depends on your model and cash position. The shorter it is, the less funding you need to grow; many small businesses aim to recover it within a few months, but treat that as a guide, not a rule.
Does it work for service businesses without recurring revenue?
Yes. Choose the "services" model and use the share of clients who rehire you or refer others as your retention input.
What is this prompt for?
Find out whether each customer makes or loses you money: calculate contribution margin, CAC, LTV, LTV:CAC ratio and payback months, with a sensitivity analysis.
Which AI tools does it work with?
It is designed for ChatGPT, Claude, Gemini and Microsoft Copilot. We have not verified it in these tools yet, so results may vary between them.
How do I customize the prompt?
Click “Customize” and fill in the variables (Business model, Average revenue per customer or order, Variable costs, Acquisition spend and new customers and Retention). The text updates instantly and you can then copy it in one click. Values are stored only in your browser.
Do I need experience to use it?
It is advanced: it is meant for people with experience in the topic who can evaluate and adjust the result.
Is this prompt free?
Yes. Every HomeCasa Prompts prompt is free, with no sign-up or subscription. You can also use them in professional projects.
Can I trust the AI output?
Treat it as a high-quality draft: always check data, figures and important claims before publishing or making decisions.