F10. Building a Simple Cash Flow and Unit Economics Spreadsheet
After this lesson you can
- Lay out every assumption in one labeled tab, separate from calculations
- Build monthly cash in, cash out, net cash and a running balance that reflects payment delays
- Calculate runway, contribution margin, payback and lifetime value
- Run one-at-a-time sensitivity checks and a downside scenario
- Name the assumption a model depends on most and the evidence to gather next
Video coming soon
Videos are planned to publish from December 2026.
A hands-on build of a four-tab spreadsheet, using only invented numbers, that treats a financial model as a logic test rather than a prediction. It walks through labeled assumptions, monthly cash in and out with runway, contribution margin, payback and lifetime value, and a downside scenario with one-at-a-time sensitivity checks. It teaches no tax or accounting treatment.
Questions and answers
Questions a learner would ask about this lesson. Think through your own answer before you open each one.
- Is a spreadsheet model a forecast of what will happen?
Show answer
No. The lesson treats a model as a logic test, not a prediction, and every number in the video is invented. Cash and profit are different things, and the video teaches no tax or accounting treatment. Questions about how rules apply to a real situation belong with an accountant or tax professional.
- How should the workbook be organized?
Show answer
Four tabs: Assumptions (every input, labeled, with a source or status), Cash (monthly cash in, cash out and balance), Unit Economics (margin, payback and lifetime value), and Outputs (key results and a scenario log). Numbers flow one way, from inputs to results, and formulas never contain hard-coded values typed directly into them.
- What is runway?
Show answer
The lesson defines runway as the number of months until cash runs out at the current net burn. In Founder A's model, 1,920 dollars at the end of month two divided by 360 dollars of net burn gives about 5.3 more months. Burn changes, so it is recalculated every month.
- What are contribution margin and payback?
Show answer
Contribution margin is price minus all variable costs of delivering and serving one customer for one period. In the example, 150 dollars minus 30 dollars gives 120 dollars per clinic per month. Payback divides the acquisition cost of 1,680 dollars by that margin, which gives 14 months.
- What is the difference between a scenario and a sensitivity check?
Show answer
A scenario is a full set of assumptions telling one story, such as a base case or a downside case where several things go worse. A sensitivity check changes one assumption, keeps the rest, records the result and changes it back. It shows which input matters most.
Practice quiz
- Question 1Why keep assumptions on a separate tab?
- Question 2In the model, runway is calculated from what?
- Question 3Founder A's runway drops from nine months to four when only the payment delay changes. What does this tell Founder A?
- Question 4Price is 150 dollars per clinic per month and variable cost is 30 dollars per clinic per month. What is the contribution margin?
- Question 5Acquisition cost is 1,680 dollars per clinic and contribution margin is 120 dollars per month. What is the payback period?
- Question 6With a 120-dollar monthly margin and a conservative guess that a clinic stays 24 months, what is the conservative lifetime value?
- Question 7What is a hard-coded value?
- Question 8Founder A's lifetime value to acquisition cost ratio is 1.7 in the conservative case and 10 in the optimistic case. What does the lesson conclude?
- Question 9In Founder B's three-row model, clients pay 60 days after delivery and software costs 80 dollars a month. Why is the running balance negative in months one and two?
- Question 10In the 2020 survey of 885 institutional venture capital investors cited in the lesson, what did investors rate as somewhat more important than the product or technology?
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