Monte Carlo cash flow simulator
A Monte Carlo simulation of your business cash flow, in the browser, with no spreadsheet and no account: 5,000 seeded, reproducible monthly paths from your own figures, the full probability range, and a receipt for every run. It refuses questions it cannot answer.
Built for people who already think in distributions
If you have reached this page you already know a single projection is a story, not a forecast. What is usually on offer is a spreadsheet template with a RAND() column, or a portfolio tool built for retirement planning. This is neither. The model is a monthly cash recurrence — revenue with stated growth and volatility, costs with stated growth — walked 5,000 times from a fixed seed; the same figures and seed give the same paths anywhere, so a result can be checked rather than believed. The maths is open on the glass-box page, any receipt can be re-run on the reproduce page, and the released model is held to its published version by an automated suite on every release. What it will not do: fill in an input you have not given, route a question to a nearby model and answer as if it fitted, or show an accuracy figure before there is one.
A worked run
PROBABLY SAFE, WATCH IT
60–70%
probability the balance stays above zero over 12 months, across 5,000 simulated futures
- Months before cash runs out — 1 in 10 futures
- 9
- Median future
- 12+
- Best 1 in 10
- 12+
- Scenarios — Expected
- Expected 65%
- Upside
- Upside 82%
- Downside
- Downside 45%
- Stress
- Stress 22%
- What moves it most
- Monthly costs
- Where the odds flip
- The median path reaches the horizon at or above 0.1%/month revenue growth; you stated 2%.
- Evidence quality
- moderate
Seed 564 · receipt rw_52f9a7c3_234 · runway@1.0.1. Same figures, same seed, same answer — reproduce it or verify the receipt.
Worked example, computed by the engine at build time. Edit the figures and it recomputes here, in your browser.
Growth and volatility are marked as assumptions because that is what they are; cash, revenue and costs are facts if a bank statement backs them. The engine ranks which input moves the answer most, so the argument you need to have is about that input and not about the others. If you came for the plain formula first, the cash runway calculator starts there and arrives at this same engine. For the complete record — labelled evidence, the stress case, a sealed receipt and the outcome when it arrives — open the decision simulator.
Questions people ask
What does a Monte Carlo cash flow simulation do?
It runs the same monthly cash model thousands of times with random variation in the inputs that vary — here, revenue — and counts the outcomes. The result is a distribution of futures, not one projection.
Is the simulation reproducible?
Yes. Every run is seeded: the same inputs and the same seed produce the same 5,000 paths and the same answer, on any machine. Each result carries a receipt that anyone can re-run on the reproduce page.
Do I need a spreadsheet or an account?
No. The simulation runs in your browser, there is no account and no card, and your figures never leave your device: this page has no Copilot box, so nothing you type here is sent anywhere.
What will it refuse to do?
It refuses to run on unknowns, refuses to answer questions the model does not cover, and publishes no accuracy percentage for any model until ten real outcomes have resolved. A blank is more honest than an invented number.