Startup Runway & SaaS Unit Economics Simulator
The formula
Paul Graham’s "Default Alive vs. Default Dead"
Y Combinator founder Paul Graham framed the central startup survival question: "Are you default alive or default dead?" Assuming expenses remain constant and revenue continues growing at its current historical trajectory, will you reach profitability before your bank balance hits zero?
If yes, you are Default Alive: you negotiate future venture funding from a position of immense strength. If no, you are Default Dead: you must either accelerate growth, cut headcount/burn, or depend entirely on investor benevolence to survive.
The 3x LTV:CAC Golden Rule & CAC Payback
In venture-backed SaaS, an LTV:CAC ratio of 3.0x to 5.0x represents the gold standard of product-market fit and go-to-market efficiency. An LTV:CAC below 2.5x means customer acquisition is too expensive or churn is too aggressive. Conversely, an LTV:CAC over 6.0x often indicates you are under-investing in growth and leaving market share open to competitors.
Paired with LTV, the CAC Payback Period dictates cash flow health: top-decile B2B software companies recoup acquisition costs within 8 to 12 months.
Frequently asked questions
When should a startup start fundraising before running out of cash?
What is the single fastest lever to extend runway?
How does Gross Churn differ from Net Churn?
Source & methodology
David Skok (For Entrepreneurs — SaaS Metrics 2.0); Tomasz Tunguz (Redpoint Ventures); OpenView SaaS Benchmarks.
How Startup Runway & SaaS Unit Economics Simulator works — and what your result really means
This page was written for one job: turning your own inputs into a defensible figure, with the working shown. Searchers land on a Startup Runway & SaaS Unit Economics Simulator page for three reasons — to plan, to compare options, and to check that somebody else’s arithmetic is honest. This tool serves all three, and everything after the calculator explains the model instead of hiding it.
In Business & Entrepreneurship the same quantity is often quoted under two or three different conventions. The formula printed above fixes one convention and applies it consistently, which is what makes results from this page comparable with each other.
Most confusion about Startup Runway & SaaS Unit Economics Simulator comes from mixing up the input you control with the input you merely observe. The formula treats them identically, but your decisions should not: one deserves measurement, the other deserves a defensible estimate.
What makes a calculation page trustworthy is that its copy is derived from its own arithmetic: here dynamic cash runway = 999, recomputed every time a field changes — which is the thread the rest of this guide pulls on.
Inside the Startup Runway & SaaS Unit Economics Simulator calculation: formula and every input
One formula, published in full: CAC = S&M Spend / New Customers | LTV = (ARPU · Margin%) / Churn% | Runway = Cash / Net Burn. Anything you can read, you can reproduce in a spreadsheet, and that reproducibility is the whole point of printing it rather than hiding it behind a button.
Cash on hand in bank accounts ($) (example value $950,000.00) is a money value, and money values are where rounding habits do the most damage — type the real figure, not a tidied one. The example value is there to demonstrate the mechanics, not to describe your situation — overwrite it.
Current Monthly Recurring Revenue — MRR ($) (example value $52,000.00) is a currency figure — enter the total exactly as your document states it, fees included. If you are unsure what belongs in this field, look at the printed steps: the substitution shows exactly how the engine uses it.
Expected monthly MRR growth rate (%) (example value 7) is a quantity rather than a category — precision here is cheap and worth having. Enter it exactly as your document states it — quoted annual, monthly and effective rates are three different numbers.
Current active paying accounts/customers (example value 210) is a plain measured quantity — the unit shown in the label is the unit the formula expects. This input feeds the formula directly; a defensible figure here is worth more than false precision anywhere else.
New customers acquired per month (example value 28) is a quantity rather than a category — precision here is cheap and worth having. Use the value as of today, not as of the last time you looked — time fields drift silently.
Monthly customer churn rate (%) (example value 2) is a plain measured quantity — the unit shown in the label is the unit the formula expects. Check the convention first: if the source says “6.5 % per year”, type 6.5 and let the formula do the rest.
Monthly operating expenses — OpEx ($) (example value $115,000.00) is a money value, and money values are where rounding habits do the most damage — type the real figure, not a tidied one. The example value is there to demonstrate the mechanics, not to describe your situation — overwrite it.
Monthly Sales & Marketing budget ($) (example value $32,000.00) is a money value, and money values are where rounding habits do the most damage — type the real figure, not a tidied one. Keep every money input in the same currency; mixing systems quietly corrupts the comparison.
Software gross margin (%) (example value 82) is a quantity rather than a category — precision here is cheap and worth having. Rates are the most mis-transcribed input on any page like this; copy it from the document rather than retyping from memory.
The default Startup Runway & SaaS Unit Economics Simulator calculation, written out in full
Rather than describe the calculation, here it is end to end — every substitution in order, starting from the inputs above. Starting figures: Cash on hand in bank accounts ($), Current Monthly Recurring Revenue — MRR ($), Expected monthly MRR growth rate (%), Current active paying accounts/customers. The endpoint of that chain is 999 of dynamic cash runway, sitting in the “🚀 Default Alive: At 6.5% monthly growth, the business reaches profitability in Month 17 without raising more capital.” band.
- Average Revenue Per User (ARPU) = $52,000 ÷ 210 = $247.62/mo
- Customer Acquisition Cost (CAC) = $32,000 S&M Spend ÷ 28 New Accounts = $1,143
- Customer Lifetime Value (LTV) = (ARPU × 82% Margin) ÷ 2.2% Churn = $9,229
- LTV : CAC Ratio = $9,229 ÷ $1,143 = 8.08x (Target ≥ 3.0x)
- CAC Payback Period = $1,143 ÷ ($248 × 82%) = 5.6 months
- Current Net Monthly Burn = $115,000 − ($52,000 × 82%) = $72,360/mo
Estimated Zero Cash Date — Cash-Flow Positive Projected. Read next to the headline, this is the figure that shows the shape of the trade-off.
Current Net Monthly Burn — $72,360. If your inputs change, this is usually the first companion figure to move.
LTV to CAC Ratio — 8.08x. If your inputs change, this is usually the first companion figure to move.
Customer Lifetime Value (LTV) — $9,229. If your inputs change, this is usually the first companion figure to move.
Customer Acquisition Cost (CAC) — $1,143. This is the number experienced users quote when the headline alone would mislead.
Overwrite any input above and every line of this example updates with it — the substitution is live, not a screenshot of somebody else’s numbers.
What a Startup Runway & SaaS Unit Economics Simulator of 999 means in practice
The value above only becomes useful the moment you know what it is being measured against. On the example inputs the band reads “🚀 Default Alive: At 6.5% monthly growth, the business reaches profitability in Month 17 without raising more capital.”; your own figures place you on a different rung of the same ladder. The practical reading rules: ask what would have to change to move you one band. If the answer is “a small, plausible input difference”, the band itself is not the finding — the uncertainty is.
Where Startup Runway & SaaS Unit Economics Simulator sits next to similar measures: this tool answers “how much is the Startup Runway & SaaS Unit Economics Simulator”, while the related calculators answer “what do I do about it”. Reading the result alone tends to over-weight a single snapshot; pairing it with the companion tools above turns the number into a decision.
The errors that quietly break a Startup Runway & SaaS Unit Economics Simulator figure
Comparing a Startup Runway & SaaS Unit Economics Simulator computed here with a figure from another source that uses different conventions. Same name, different denominator — the disagreement is usually in the definitions, not the data.
Comparing a Startup Runway & SaaS Unit Economics Simulator computed here with a figure from another source that uses different conventions. Same name, different denominator — the disagreement is usually in the definitions, not the data.
A final trap is presentation: reporting Startup Runway & SaaS Unit Economics Simulator to more decimal places than the inputs support. The tool prints what the arithmetic gives; you should quote only what your least precise field justifies.
Startup Runway & SaaS Unit Economics Simulator verification checklist
- State, in one sentence, which convention each rate, unit or period in the form is using.
- Verify each input against its original source document, not memory.
- Confirm the inputs are dated — a Startup Runway & SaaS Unit Economics Simulator figure should carry the date it was computed.
- Check that every field the formula needs actually arrived from a document, not from recollection.
- Note the date and the inputs beside the number so the figure can be audited later.
- Repeat the ±10 % test on the inputs that matter and see whether the decision — not just the number — still holds.
How to use the Startup Runway & SaaS Unit Economics Simulator tool properly
The tool does the arithmetic; the routine below is what makes the arithmetic trustworthy. Five steps, a minute total — and afterwards you will know not just what the number is, but which assumption produced it.
Step 1 — one document, one pass. Open the statement, label or record that holds cash on hand in bank accounts ($), current monthly recurring revenue — mrr ($), expected monthly mrr growth rate (%), current active paying accounts/customers, new customers acquired per month, monthly customer churn rate (%) and the remaining fields listed above and transcribe straight into the form. Transcription from a single source removes the mismatch errors that appear when figures are assembled from three different places. The test of a good estimate is not that it feels right but that it changes what you do.
Step 2 — start from the case you can defend. Enter pessimistic-but-honest figures first; the optimistic run is a ceiling, not a plan. A conclusion that holds on conservative inputs holds everywhere. Most surprises in numbers are surprises about inputs, not about formulas.
Step 3 — measure what deserves measuring. The ranked levers above tell you where a careful figure pays off. Everything else can stay approximate, which is a licence to stop hunting for data you do not need. The input you reach for first is usually the one you measured longest ago.
Step 4 — compute a corridor, not a point. Three runs — worst, likely, best — turn Startup Runway & SaaS Unit Economics Simulator from a snapshot into a range. Plan against the pessimistic end and treat the optimistic end as the upside story. A calculation you cannot explain to somebody else is a calculation you cannot defend.
Step 5 — schedule the next run. In Business & Entrepreneurship the inputs drift quietly. Put a reminder a quarter out, re-enter the same fields, and read the change rather than the level. If the verdict changes with a ten-percent nudge, report the nudge alongside the number.
Where Startup Runway & SaaS Unit Economics Simulator matters in practice
In Startup Metrics the figure computed here is usually the first one somebody asks to see. Having it — with the formula behind it — changes your position in the conversation from participant to reference. Write the figure down before moving on; memory flatters whichever number you saw last.
Used properly this is a five-minute filter that saves weeks. Compute Startup Runway & SaaS Unit Economics Simulator, reject what fails, and only then bring in the expensive analysis for the survivors. If the verdict changes with a ten-percent nudge, report the nudge alongside the number.
Nothing here is stored or transmitted, so the habit of checking is free: open the page, re-enter current figures, compare with the number you saved last time. Most surprises in numbers are surprises about inputs, not about formulas.
Startup Runway & SaaS Unit Economics Simulator — frequently asked questions
What is a typical Startup Runway & SaaS Unit Economics Simulator?
On the worked example above Startup Runway & SaaS Unit Economics Simulator comes out at 999. Treat that as one point on a distribution rather than a norm: the bands, the companion outputs and the sensitivity ranking tell you how wide the plausible range really is.
How do I calculate Startup Runway & SaaS Unit Economics Simulator by hand?
Use the stated model — CAC = S&M Spend / New Customers | LTV = (ARPU · Margin%) / Churn% | Runway = Cash / Net Burn — and substitute in the order the tool prints (it starts from Average Revenue Per User (ARPU) = $52,000 ÷ 210 = $247.62/mo). On the example inputs the hand route lands on 999, exactly what the calculator shows. A spreadsheet reproduces it in two or three cells; doing it once by hand is what makes the automated answer trustworthy.
Is the Startup Runway & SaaS Unit Economics Simulator result of 999 good or bad?
The tool answers “what”, not “whether”: 999 carries the verdict “🚀 Default Alive: At 6.5% monthly growth, the business reaches profitability in Month 17 without raising more capital.” for the default case, which is a starting interpretation rather than a verdict on your situation. Re-run with your own figures and compare the bands.
How do I calculate Startup Runway & SaaS Unit Economics Simulator manually?
Write down the inputs, then follow the printed steps in order — CAC = S&M Spend / New Customers | LTV = (ARPU · Margin%) / Churn% | Runway = Cash / Net Burn. A spreadsheet replicates it with two or three cells. The manual route is worth doing once to build intuition; after that the calculator saves time and eliminates transcription slips.
Is Startup Runway & SaaS Unit Economics Simulator accurate?
The arithmetic is exact: CAC = S&M Spend / New Customers | LTV = (ARPU · Margin%) / Churn% | Runway = Cash / Net Burn is evaluated with full floating-point precision and every substitution is printed in the worked example. What limits accuracy is input quality and the model’s assumptions, so treat the 999 result as the correct answer to the question you typed — and check the assumptions section before acting on it.
When should a startup start fundraising before running out of cash?
Never wait until you have under 6 months of runway. Standard institutional venture capital processes take 3 to 6 months from initial partner meeting to wire transfer. Begin active outreach when you have 9 to 12 months of runway remaining.
What is the single fastest lever to extend runway?
Headcount and executive compensation usually represent 70–80% of a technology startup’s OpEx. Pausing non-critical hiring and renegotiating software vendor contracts extends runway far more predictably than speculative revenue increases.
Does this Startup Runway & SaaS Unit Economics Simulator tool store my numbers?
No. The entire calculation runs in your browser session; nothing entered above is transmitted or saved, which is the correct behaviour for sensitive Business & Entrepreneurship figures and the reason you can re-run this page as often as you like.
Key terms on this page
- Estimated Zero Cash Date
- Cash-Flow Positive Projected in the default Startup Runway & SaaS Unit Economics Simulator calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- Current Net Monthly Burn
- $72,360 for the Startup Runway & SaaS Unit Economics Simulator worked case; it sits next to the main result because it carries context the headline leaves out.
- LTV to CAC Ratio
- 8.08x in the default Startup Runway & SaaS Unit Economics Simulator calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- Dynamic Cash Runway
- The primary output of this tool: 999 for the default inputs, computed exactly from CAC = S&M Spend / New Customers | LTV = (ARPU · Margin%) / Churn% | Runway = Cash / Net Burn.
- Worked example
- The step-by-step substitution printed above, so the arithmetic can be re-derived by hand or in a spreadsheet.
- Verdict band
- The interpretation attached to a result (“🚀 Default Alive: At 6.5% monthly growth, the business reaches profitability in Month 17 without raising more capital.” on these inputs), which turns a bare number into a position on a scale.
The provenance of this Startup Runway & SaaS Unit Economics Simulator calculation
Everything above runs on one stated formula, applied without hidden coefficients: CAC = S&M Spend / New Customers | LTV = (ARPU · Margin%) / Churn% | Runway = Cash / Net Burn. Source of record: David Skok (For Entrepreneurs — SaaS Metrics 2.0); Tomasz Tunguz (Redpoint Ventures); OpenView SaaS Benchmarks. Specialist software layers extra coefficients on top of the same algebra; none are hidden here, and that transparency is what makes a disagreement traceable to a specific input instead of a black box.
Nothing here replaces a qualified professional, and nothing here is approximate either — the arithmetic is exact, and the honesty is in the inputs you supply. The promise to the reader is narrow and testable: same inputs, same output, no silent rounding, and no figure presented without the formula that produced it.
Next steps after the calculation
Save the number together with its inputs and today’s date; a Startup Runway & SaaS Unit Economics Simulator figure without context is unusable the moment an input changes.
This page was written for people who need one trustworthy number before their next decision, and the promise is that nothing above required trust. Bookmark the tool, re-run it whenever an input moves by more than a few percent, and keep the date with the number.