Understanding Your Forecast's Flow: From Inputs to Net Income

A financial model isn't a black box. Every number in your income statement, balance sheet, and cash flow statement traces back to a set of assumptions you made about your business. Understanding that chain — how inputs flow through to outputs — is what separates founders who use their model as a decision tool from those who just update it before board meetings.

Where it starts: acquisition assumptions

For most businesses, the model starts with customer acquisition. How many new customers do you expect to acquire each month? What does it cost to acquire them? How do you expect that number to grow?

These inputs drive everything downstream. Your revenue projection is a function of how many customers you have and what they pay. Your sales and marketing expense is a function of how aggressively you're acquiring them. Your headcount plan is a function of how many customers you need to support.

Get the acquisition assumptions wrong and every output in your model is wrong. This is why investors spend so much time on the top of the funnel — it's the foundation everything else is built on.

Revenue: the first output

Once you have your customer count and pricing, revenue is straightforward: customers multiplied by average revenue per customer. For subscription businesses, you also need to account for churn — customers who cancel each month reduce your active customer base and therefore your revenue.

The relationship between new customer acquisition, churn, and net revenue growth is one of the most important dynamics in a SaaS model. A business acquiring 100 new customers per month with 5% monthly churn will eventually plateau at 2,000 customers, regardless of how long it operates. Understanding that ceiling — and what it takes to raise it — is a core function of the model.

Costs: the second layer

Costs in a financial model typically fall into two categories: cost of goods sold (COGS) and operating expenses (OpEx). COGS are the costs directly associated with delivering your product or service — hosting, payment processing, customer support. OpEx covers everything else: sales, marketing, R&D, G&A.

The relationship between revenue and COGS gives you gross margin — the percentage of revenue left after direct costs. Gross margin is a fundamental indicator of business model health. SaaS businesses typically target 70–80% gross margins. Services businesses often run at 30–50%.

Operating expenses are where most of your headcount costs live. As you grow, OpEx tends to scale with headcount, which is why your staffing plan is such a critical input to the model.

The bottom line: net income

Subtract COGS and OpEx from revenue and you get operating income (EBIT). Add interest income and subtract interest expense and taxes and you get net income — the bottom line.

For early-stage startups, net income is almost always negative. That's expected. What matters is the trajectory: is the loss shrinking as a percentage of revenue? Is gross margin improving? Is the path to profitability visible at some reasonable scale?

Cash flow: the reality check

Net income and cash flow are not the same thing. Net income is an accounting concept; cash flow is what actually hits your bank account. The difference comes from timing — when you recognize revenue versus when you collect it, when you recognize expenses versus when you pay them.

For most early-stage startups, the cash flow statement is the most important financial statement. It's the one that tells you whether you're going to run out of money before you reach profitability.

Horizon's Model Guide visualizes this entire flow — from acquisition inputs through revenue, costs, and down to net income and cash position — so you can see exactly how your assumptions connect to your outcomes.

If you want to go deeper on how the Income Statement, Balance Sheet, and Cash Flow Statement connect to each other — and what to look for in each one — read the Understanding Your Financial Statements guide.