Key takeaways
- Four numbers predict survival better than forty metrics: DSO (money coming in), net burn (money going out), runway (the gap and how long you have), and gross margin variance (whether the economics are drifting).
- DSO = (AR ÷ Monthly Revenue) × 30. Healthy is under 45 days; a steady upward drift is an early collections warning.
- Runway = Cash ÷ Monthly Net Burn. Healthy is 18+ months; under 12 is danger; under 6 is an emergency. Use a 3-month trailing average for burn to smooth one-off expenses.
- Gross margin variance matters more than the snapshot — a decline of more than 3 points in a quarter should trigger an investigation, because margin is very hard to improve once the pattern is set.
If you’ve built the 13-week cash flow model, you now have a spreadsheet full of numbers. Weeks, rows, balances, projections. That’s the right tool. But a tool without interpretation is just data.
There are four numbers — inside that model and across your business — that tell you more about your survival odds than anything else. Not forty metrics. Not a full dashboard. Four.
DSO. Cash burn. Runway. Gross margin variance.
Each one is a different angle on the same question: are the fundamentals healthy, or is something quietly breaking? Together, they tell you whether you’ll be in trouble in six months — before the bank account does.
Why these four?
Early-stage founders often respond to financial anxiety by tracking more: more metrics, more reports, more data points. The instinct makes sense. More information feels like more control.
But most financial metrics at a 3–5 person company are noise. They fluctuate for reasons that don’t matter, require context to interpret, and distract from the handful of signals that actually predict whether the business is heading toward stability or trouble. These four numbers catch different kinds of problems:
- DSO catches problems in how fast money is coming in
- Cash burn catches problems in how fast money is going out
- Runway catches the gap between the two — and how long you have before it closes
- Gross margin variance catches whether the economics of the business itself are drifting
You can track all four in under 30 minutes a week once the 13-week model is running. Here’s what each one means and what to watch for.
1. DSO — Days Sales Outstanding
DSO measures the average number of days between sending an invoice and receiving the payment. It reveals how quickly a company converts credit sales into cash — and is one of the earliest indicators of cash flow stress before it hits the bank.
How to calculate it: (Accounts Receivable ÷ Monthly Revenue) × 30. If you have $45,000 in outstanding invoices and monthly revenue of $38,000: ($45,000 ÷ $38,000) × 30 = 35 days.
| DSO | |
|---|---|
| Healthy | Under 45 days |
| Watch | 45–60 days |
| Danger | Over 60 days |
For SaaS and B2B professional services, average DSO runs 30–45 days. Under 30 is strong. A steady drift upward — 32 days last month, 38 days this month, 44 days now — is an early warning that something is changing in how clients are paying, worth investigating before it becomes a collections problem.
One practical note with a real impact: sending invoices within 24 hours of delivery reduces DSO by 5–8 days on average. The same research shows that contacting a client within 24 hours of a missed payment yields a 65% collection success rate — compared to 15% if you wait two weeks. Fast invoicing and fast follow-up are two of the cheapest cash flow improvements available to a small team.
2. Net burn rate
Net burn is the amount of cash your business actually consumes each month after revenue. It’s the real rate at which your bank account is shrinking.
How to calculate it: Monthly Expenses − Monthly Revenue = Net Burn. If monthly expenses are $47,000 and revenue is $38,000, net burn is $9,000/month.
This is different from gross burn, which is total expenses without subtracting revenue. Gross burn matters for understanding your cost structure. Net burn is what determines how fast cash is depleting — and it’s the number that connects directly to runway.
The right burn rate isn’t a universal number. What matters more than the absolute figure is the trend and the quality of the burn. A $9,000/month net burn funding a hire who generates $15,000 in new monthly revenue within 90 days is productive burn. A $9,000/month net burn spread across unused SaaS tools and a contractor relationship delivering nothing is noise burn. Same number, fundamentally different situations.
The danger signal isn’t burn itself — it’s burn accelerating faster than revenue is growing. If net burn is rising month-over-month while revenue stays flat, the gap between what you’re spending and what’s coming in is widening. That’s the pattern to catch early, not after it becomes a cash crisis. One practical technique: use a 3-month trailing average rather than a single month’s figure. One-off expenses — a legal bill, a recruiting fee, a large software renewal — distort any single month. The trailing average smooths those anomalies and gives you a cleaner signal.
3. Runway
Runway is how many months your business can continue operating at current burn before cash runs out. It’s the most direct measure of how much time you have to work with.
How to calculate it: Cash on Hand ÷ Monthly Net Burn = Months of Runway. $195,000 in the bank at $9,000/month net burn = 21.7 months of runway.
| Runway | |
|---|---|
| Healthy | 18+ months |
| Watch | 12–18 months |
| Danger | Under 12 months |
| Emergency | Under 6 months |
Runway should drive the timing of your fundraise. Fundraising takes 4–6 months on average from first meeting to close — which means starting at 12 months of runway remaining is the minimum to close before you’re desperate. Starting at 18 months gives you the runway to be selective, walk away from bad offers, and raise on terms that reflect the business rather than your urgency.
The consensus among investors and startup advisors is to target 18–24 months of runway between raises — this gives you 12–18 months to operate and 6 months to fundraise without pressure.
One important note: runway is dynamic, not static. A large client payment can extend it by a month. An unexpected hire or expense can shrink it by two. The 13-week model keeps your runway estimate current — it’s not a number you calculate once and revisit quarterly.
4. Gross margin variance
Gross margin is the percentage of revenue left after you subtract the direct costs of delivering your product or service. Gross margin variance is the change in that percentage over time — and the direction of that change is what matters most.
How to calculate it: (Revenue − COGS) ÷ Revenue × 100 = Gross Margin %. If monthly revenue is $38,000 and direct delivery costs are $8,000: ($38,000 − $8,000) ÷ $38,000 = 78.9%.
For a B2B service company, COGS includes contractor costs, direct software costs tied to client delivery, and any direct fulfillment costs — not general salaries, not sales commissions, not overhead.
| Gross Margin | |
|---|---|
| Strong | Over 75% |
| Acceptable | 60–75% |
| Watch | 50–60% |
| Danger | Under 50%, or declining more than 3 points |
For B2B SaaS and services companies, healthy gross margin sits in the 70–85% range, with 80%+ considered strong. But the trend matters more than the snapshot. A decline of more than 3 percentage points in a quarter should trigger an investigation — are delivery costs rising, is pricing too low for what it costs to serve clients, or is one contract dragging the average down?
The reason this matters especially early: gross margin is very hard to improve once the pattern is set. Founders often assume scale will fix a margin problem. The data says otherwise — a company with 40% gross margins that doubles revenue doesn’t double its financial health. It doubles the cash pressure, because every dollar of growth requires significant direct cost to deliver.
All four in one view
| Metric | Formula | Healthy | Watch | Danger |
|---|---|---|---|---|
| DSO | (AR ÷ Monthly Revenue) × 30 | <45 days | 45–60 days | >60 days |
| Net Burn | Monthly expenses − revenue | Flat or declining | Rising slowly | Accelerating vs. flat revenue |
| Runway | Cash ÷ Monthly net burn | 18+ months | 12–18 months | <12 months |
| Gross Margin | (Revenue − COGS) ÷ Revenue | >75% | 60–75% | <50% or declining >3 points |
What good looks like
A founder running these four metrics weekly doesn’t wait for a crisis to understand their position. They have a clear answer to “where do we stand in 12 weeks?” — because they know their runway to the week, their burn trend, whether clients are paying faster or slower, and whether the margin is holding.
More importantly, they see problems while there’s still room to respond. DSO creeping from 32 to 48 days over six weeks is a signal, not yet a crisis — but only if someone is looking. Runway dropping from 19 months to 13 months over a quarter is a clear indicator that a fundraising conversation needs to start now, not at 8 months.
The dashboard doesn’t make the decisions. It makes the decisions legible. Reading the model correctly — knowing exactly when it’s telling you to raise, cut, or hire — is what the next part of this guide covers.
