What is Cash Flow Forecast Calculator?
A cash flow forecast projects how a business's cash balance will change over time, based on expected monthly inflows (revenue, collections) and outflows (expenses, payroll, rent, debt payments). Unlike profit, which can be recognized before cash actually changes hands, a cash flow forecast tracks the literal timing of money moving in and out of a bank account — the number that ultimately determines whether bills get paid.
This is especially critical for startups and small businesses that don't yet have steady positive cash flow. Running out of cash, not running out of profitability, is one of the most common reasons businesses fail — many profitable-on-paper companies have collapsed because they couldn't cover payroll or rent during a cash crunch.
This calculator projects a cash balance forward from a starting amount, given expected monthly inflows and outflows (with optional growth rates for each), and calculates the runway — the point at which cash would run out if nothing changes. Seeing this number early gives a business time to act: cut costs, accelerate collections, or raise financing before the situation becomes urgent.
Steps:
- Enter your current starting cash balance.
- Enter expected monthly cash inflow (revenue, collections).
- Enter expected monthly cash outflow (expenses, payroll, rent).
- Enter the number of months to project forward.
- Optionally enter monthly growth rates for inflow and outflow, then review the balance chart and runway.
Formula
Inflow(month) = Monthly Inflow × (1 + Inflow Growth %)^(month - 1)
Outflow(month) = Monthly Outflow × (1 + Outflow Growth %)^(month - 1)
Net Cash Flow(month) = Inflow(month) - Outflow(month)
Balance(month) = Balance(month - 1) + Net Cash Flow(month)
Runway = first month where Balance ≤ 0
Example: Starting cash $50,000, inflow $8,000/mo, outflow $12,000/mo, no growth
Net burn = -$4,000/mo → Runway ≈ 12.5 months
Use Cases
- Startup founders tracking runway before their next funding round
- Small business owners planning for seasonal revenue dips without running out of cash
- Finance teams building monthly cash forecasts for board or investor reporting
- Business owners deciding whether they can afford a new hire or major purchase
- Anyone modeling the cash impact of a planned expense increase or revenue slowdown
Key Benefits
- See your projected runway before cash actually becomes a problem
- Model how changes in revenue or spending growth affect your cash position over time
- Communicate cash position clearly to investors, lenders, or co-founders
- Plan hiring, purchasing, or expansion decisions around actual cash availability, not just profit
- Catch a looming cash shortfall months in advance, when more options are available to address it
Pro Tips
- Base your inflow and outflow assumptions on actual historical averages, not hopeful projections.
- Build a cash buffer into your outflow assumptions for unexpected expenses.
- Update your forecast monthly with actual results to keep the projection grounded in reality.
- Model a conservative scenario alongside your expected case to see your worst-case runway.
- If your runway is shortening, address it early — accelerating collections or cutting costs is far easier with months of lead time than weeks.
Common Mistakes to Avoid
- Confusing profit with cash — assuming a profitable month means cash is also growing
- Basing inflow projections on optimistic best-case revenue rather than realistic historical trends
- Forgetting to include irregular but predictable outflows like annual insurance or tax payments
- Not updating the forecast regularly, so it drifts further from reality each month
- Waiting until cash is critically low to act, instead of addressing a projected shortfall months in advance
Key Terms Explained
- Cash Flow: The actual movement of cash into and out of a business, distinct from accounting profit
- Runway: The number of months a business can operate before running out of cash at current burn rate
- Burn Rate: The rate at which a business spends down its cash reserves each month
- Inflow: Cash coming into the business, primarily from revenue and customer collections
- Outflow: Cash leaving the business, including expenses, payroll, rent, and debt payments
Example
A startup has $150,000 in the bank, brings in $20,000/month in revenue (growing 5% monthly), and spends $35,000/month on expenses (growing 2% monthly). The forecast shows the cash balance declining each month despite inflow growth, with runway hitting zero around month 9 — giving the founders roughly 9 months to raise financing, cut costs, or grow revenue faster.