Nobody believes a three-year forecast, including you. That's fine. Investors read your model to see whether you understand how your business works: what drives revenue, what drives cost, and when the money runs out.
1Gather the drivers
A good model is built from a few inputs everything else calculates from. Change one and the whole model updates.
| Input | Example | Where it comes from |
|---|---|---|
| Customers today | 14 | Your records |
| New customers per month, now | 4 | Last 3 months average |
| Monthly growth in new customers | 8% | Your plan, defended by a channel |
| Monthly churn | 3% | Your data, or an honest estimate |
| Revenue per customer per month | $400 | Your pricing |
| Cost to serve, % of revenue | 18% | Hosting, tools, support |
| Cost to acquire a customer (CAC) | $2,500 | Sales and marketing spend ÷ new customers |
| Team: role, salary, start month | 2 engineers in month 3 | Your hiring plan |
| Other costs | Tools, rent, legal | Your bank statements |
| Cash today, and the round | $150K, raise in month 3 | Your bank and plan |
2Build it in three tabs
- Assumptions: every input above, in one place. Color inputs blue so anyone can see what they can change.
- Monthly model, 36 columns: customers (start + new − churned), revenue, cost to serve, gross profit, payroll, other costs, net burn, funding, cash at month end.
- Summary: the headline numbers and the health checks below.
Every number outside the Assumptions tab should be a formula, never typed in. That's what lets an investor change your growth rate and watch what happens.
Build a 36-month startup financial model as an Excel file with live formulas. Tabs: Assumptions (inputs in blue), Model (monthly), Annual (years 1 to 3), Summary. My inputs: [paste the table above with your numbers]. Show monthly revenue, gross margin, burn, cash, runway, breakeven month, LTV, LTV:CAC and CAC payback. Every calculated cell must be a formula, not a typed number.
3Check the four numbers partners check
| Check | Good | Watch | Risk |
|---|---|---|---|
| Runway after the raise | 18+ months | 12 to 18 | under 12 |
| Gross margin | 50%+ (software often 70%+) | 30 to 50% | under 30% |
| LTV : CAC | 3x or more | 2 to 3x | under 2x |
| CAC payback | 12 months or less | 12 to 18 | over 18 |
LTV (lifetime value) is revenue per customer × gross margin ÷ monthly churn. CAC payback is CAC ÷ (revenue per customer × gross margin).
4Build the bad-quarter case
Partners will ask "what if growth is half what you think?" Answer before they do.
- Slower growth: copy the model, halve the growth rate and double churn.
- The round slips: in the original, move the funding three months later.
For each, read the runway. If the cash runs out before the money lands, you need a cheaper plan now, not later. Write down your trigger: "If cash falls below 9 months of burn, we pause the two planned hires."
5Size the raise from the model
Work backwards from the milestone that makes your next round easy:
- What must be true at the next round? A revenue level, a growth rate, a product milestone.
- Which month does the model hit it?
- Add about 6 months of buffer.
The raise is the total burn to that point, plus the buffer.
$[amount] gets us to [milestone] by [month], with [N] months of runway left.
Build it in Google Sheets with the structure above. Anthropic's free financial-services skills can also build models in Excel.
The raise-model skill builds the full 36-month Excel model with live formulas, health checks, benchmarks and the raise sentence from your answers.
StartWise's model builder keeps your numbers in sync with your deck and checks them against benchmarks for your industry and stage.
Do it in StartWise →What's next
Investors who like the deck and model will ask for documents. Get ahead of it: set up your data room.
Revenue, costs, team and funding in one guided flow, with scenarios, runway and SAFE conversion done right. The free steps above still work. This is the fast way.