Cash flow is the net amount of cash moving in and out of your business during a period. Positive cash flow = more cash coming in than going out (you're building reserves). Negative cash flow ("burn") = spending more than earning, depleting reserves. Cash flow differs from profit (an accounting concept based on revenue/expense recognition timing) — a business can be profitable on paper but cash-negative if customers haven't paid yet. Cash flow management is more critical to business survival than profit alone.

Runway is how many months a business can operate at current burn rate before running out of cash. Formula: Runway = Current Cash / Monthly Burn Rate. Example: $200K cash, $25K/month burn = 8 months runway. Critical metric for startups and any cash-negative business. Convention: most VCs recommend 12-18 months runway as buffer for unexpected challenges. Fundraising typically takes 4-6 months, so start fundraising when 8+ months remain to avoid desperate negotiations from weakness.

How can I improve cash flow?

Multiple levers: (1) Increase revenue. (2) Reduce expenses. (3) Collect receivables faster (clear invoicing, early payment discounts, automated reminders, factoring). (4) Negotiate longer payment terms with suppliers (net 30 → net 60 if possible). (5) Reduce inventory levels (just-in-time when possible). (6) Convert to subscription/recurring revenue (predictable cash). (7) Defer non-essential capex. (8) Establish line of credit for liquidity buffer. (9) Improve pricing where possible. (10) Reduce DSO (days sales outstanding) through better credit policies. Each lever produces measurable cash flow impact.

Burn rate is monthly cash outflow exceeding inflow — the rate at which a business is depleting cash reserves. Two types: "Gross burn" = total monthly expenses (cash going out). "Net burn" = expenses minus revenue (actual cash being lost). Net burn is more useful for runway calculations. Example: $40K expenses, $25K revenue = $15K net burn. With $150K cash, runway = 10 months. Startup-specific metric but applies to any cash-negative business. Healthy companies have $0 or negative burn rate (cash-positive).

How much cash should I keep on hand?

Depends on business type and risk profile. Established small business: 3-6 months operating expenses as emergency reserve. Startup or volatile business: 12-18 months runway. Larger company with stable cash flow: 1-3 months expenses + business credit line for liquidity. Industries with seasonal patterns: enough to weather low season + buffer. Industries with major one-time expenses (equipment failure, legal): higher reserves. Industries with predictable monthly revenue (subscription): lower reserves acceptable. Generally err on side of more cash — limits stress and bad decisions during crisis.

Cash Flow Calculator

Forecast monthly cash flow by entering revenue, expenses, and growth rate. See your net cash flow margin, burn rate if negative, and how many months of runway you have. View a month-by-month projection of cumulative cash position.

Last updated: July 28, 2026Reviewed by the CalcMountain editorial team

About this calculator

Cash flow — the net movement of money into and out of a business — is the single most important metric for business survival. Profitable businesses can fail from poor cash flow; unprofitable businesses can survive (temporarily) with strong cash flow. Understanding the distinction between profit (accounting concept) and cash flow (actual money) is fundamental: a business can show $200K profit on paper while having $0 in the bank if customers haven't paid yet, while inventory and payroll have been paid.

Most small business failures stem from cash flow problems, not unprofitability. Common patterns: rapid growth (more revenue requires more upfront inventory/labor before customer payments arrive — "growing yourself broke"), seasonal mismatch (revenue concentrated in some months but expenses are constant), customer payment delays (B2B businesses often wait 30-90 days for payment), and unexpected expenses (equipment failure, legal issues, lost customer). Even profitable businesses can be wiped out by 30-60 days of cash flow squeeze. The classic adage: "Revenue is vanity, profit is sanity, cash flow is reality."

This calculator projects monthly cash flow over your selected horizon, modeling revenue growth, all expense categories, taxes, and cumulative cash position. Use it for: understanding your true financial runway (months until cash runs out at current burn rate), planning for growth (when do you need outside capital?), making hire/spend decisions (can you afford this commitment given cash trajectory?), and stress-testing different scenarios (what happens if revenue drops 20%?). For startups especially, runway tracking is the most important single metric — knowing exactly how many months remain at current spend forces honest prioritization. Strong businesses maintain 3-6 months of operating cash; startups often need 12-18 months runway to weather unexpected challenges.

Formula

Monthly Cash Flow components: Revenue (with growth): Revenue × (1 + Monthly Growth Rate)^Month Monthly Growth Rate = (1 + Annual Growth Rate)^(1/12) − 1 Gross Profit = Revenue − COGS Operating Cash Flow = Gross Profit − Operating Expenses − Payroll − Loan Payments Pre-Tax Cash Flow = Operating Cash Flow (income tax calculated after) Tax = MAX(0, Operating Cash Flow × Tax Rate) Net Monthly Cash Flow = Operating Cash Flow − Tax Cumulative Cash Position: Beginning Cash + Sum of Monthly Cash Flow through Month N Runway calculation: If Net Monthly Cash Flow is negative (burn): Runway = Initial Cash / |Monthly Burn| If positive: infinite runway (cash growing) Example: $25K monthly revenue, 10% annual growth, $8K COGS, $5K opex, $7K payroll, $1K loan, 20% tax, $50K initial cash, 12-month projection. Monthly growth: (1.10)^(1/12) − 1 = 0.797% per month Month 1: Revenue: $25,000 COGS: $8,000 → Gross profit: $17,000 Opex + Payroll + Loan: $13,000 Operating cash flow: $4,000 Tax (20%): $800 Net cash flow: $3,200 Cash position end of month 1: $50,000 + $3,200 = $53,200 Month 6 (with growth): Revenue: $25,000 × 1.00797^5 = $26,012 Operating cash flow: $26,012 − $8,000 − $13,000 = $5,012 Tax: $1,002 Net cash flow: $4,010 Cash position: progressively higher Month 12: Revenue: $25,000 × 1.00797^11 = $27,277 Operating cash flow: $6,277 Tax: $1,255 Net cash flow: $5,022 Total accumulated additional cash over year: ~$48,000 Cash position end of year 1: ~$98,000 Burn rate scenario: Same business but $35K monthly expenses (instead of $21K profitable): Net monthly burn: $25K − $35K − $1K = −$11K/month (after no tax owed due to loss) Plus growth in expenses if growing team faster than revenue. Runway at $50K cash, $11K/month burn: $50K / $11K = 4.5 months Cash flow vs. profit distinction: Profit (Income Statement): Revenue − All Expenses (recognized when earned/incurred) Cash Flow (Cash Flow Statement): Actual money in/out (recognized when received/paid) A business can: Be profitable but cash-negative (customers slow to pay, inventory tying up cash) Be unprofitable but cash-positive (large depreciation expense, customer prepayments) Both matter for different decisions: Profit → long-term sustainability and tax planning Cash flow → short-term survival and operational capacity Working capital impact: Accounts Receivable (customers owe you) — increases tie up cash Inventory — increases tie up cash Accounts Payable (you owe suppliers) — increases free up cash True cash flow includes these working capital changes. This calculator simplifies by assuming receipt timing matches revenue recognition.

How to use this calculator

Enter current monthly revenue (last month's revenue is typical starting point).
Enter expected annual revenue growth rate. Use 0% if you're uncertain — conservative is better than optimistic for cash projection.
Enter COGS (cost of goods sold / direct production costs).
Enter operating expenses (rent, utilities, software, marketing, etc.).
Enter payroll and benefits separately (largest expense for most small businesses).
Enter loan/debt service payments.
Enter effective tax rate (corporate or pass-through; consult accountant).
Enter current cash on hand.
Select projection period (12 months for typical planning; 6 months for short-term cash crunch analysis; 18-24 months for longer-term planning).
Review monthly cash flow, cumulative cash position, and runway projection.
Stress test by entering pessimistic scenarios: revenue 20% lower, expenses 10% higher. Does the business survive?
For startups: aim for 12-18 months runway as buffer against unexpected challenges.
For established businesses: maintain 3-6 months operating cash as reserve.
Update projection monthly — actual results vs. projection reveals forecast accuracy and emerging issues early.

Worked examples

Profitable small business

$25K monthly revenue, 10% annual growth, $8K COGS, $5K opex, $7K payroll, $1K loan, 20% tax, $50K cash. Month 1 net cash flow: $3,200 (positive) Year 1 ending cash: ~$98,000 (cash growing) Runway: infinite (cash positive) Healthy business. 13% net cash flow margin. Building cash reserves over time. Could absorb modest setbacks without crisis. Improvement opportunities: invest excess cash in growth (marketing, additional payroll for capacity), build emergency reserve to 6 months ($120K target = 4-5 months of runway), or distribute to owners.

Startup burning cash

$15K monthly revenue, 30% annual growth, $5K COGS, $8K opex, $20K payroll, $0 loan, 0% tax (operating loss), $200K seed funding. Month 1 net cash flow: $15K − $5K − $8K − $20K = −$18K/month (burning) Runway: $200K / $18K = 11.1 months Concerning but typical early-stage startup. Need to either: grow revenue faster than expense growth, raise additional capital, or cut burn rate. With 30% annual growth, monthly revenue Month 6 ~$17K, Month 12 ~$19.5K. If expenses stay flat: Month 6 burn: $17K − $33K = −$16K Month 12 burn: $19.5K − $33K = −$13.5K Improving but still negative. Need to either accelerate revenue growth or reduce burn by hiring more selectively. Or raise Series A before runway expires (typical fundraising takes 4-6 months — start when ~8 months runway remains).

Seasonal business stress test

Garden center: $80K revenue April-October (peak season), $15K revenue November-March (off-season). $30K monthly fixed costs. Peak months (7 months): $80K × 7 = $560K revenue, $30K × 7 = $210K cost = $350K cash Off-season (5 months): $15K × 5 = $75K revenue, $30K × 5 = $150K cost = −$75K cash Annual net: $275K profit. But cash position swings massively: End of October (peak): Cash high (~$200K+ accumulated from peak) End of March (off-season end): Cash low (potentially negative if reserves insufficient) Seasonal businesses need to: build cash reserves during peak (don't spend all peak revenue), plan financing for off-season (line of credit), and manage carefully through cash low points. Monthly cash flow planning is essential, not just annual P&L.

When to use this calculator

Use this calculator for monthly business cash flow planning, runway projection for startups, stress testing financial scenarios, planning growth and hiring decisions, or assessing whether to seek financing.

Pair with profit-margin (profitability analysis), break-even (revenue threshold modeling), and burn-rate (startup-specific cash analysis).

Important cash flow considerations:

1. **Cash flow ≠ profit.** Profitable businesses can fail from poor cash flow; unprofitable businesses can survive temporarily with strong cash flow. Both matter for different purposes.

2. **Most small business failures are cash flow failures.** Not unprofitability per se. Sound cash management prevents most failure modes.

3. **Working capital ties up cash.** Receivables (customers owe you) and inventory absorb cash. Growing businesses often need more working capital — "growing yourself broke" pattern.

4. **Receivables aging matters enormously.** 30-day customers vs. 90-day customers produce dramatically different cash positions for same revenue. Track DSO (days sales outstanding) actively; collect aggressively.

5. **Payable terms are negotiating opportunity.** Net 30 vs. net 60 from suppliers shifts cash flow by ~$X per month per $Y of payables. Negotiate longer terms when possible.

6. **Maintain cash reserves.** Established businesses: 3-6 months operating expenses. Startups: 12-18 months runway. Reserves absorb unexpected challenges without forcing bad decisions.

7. **Inventory is cash in disguise.** $50K of inventory is $50K of unavailable cash. Just-in-time inventory management improves cash flow but requires reliable suppliers.

8. **Subscription/recurring revenue improves cash flow.** Predictable monthly cash makes planning much easier than transaction-based revenue. Why SaaS valuations exceed equivalent-revenue traditional businesses.

9. **Personal vs. business cash separation.** Small business owners often blur personal and business cash. Sets up tax problems and obscures true business performance. Maintain strict separation.

10. **Lines of credit are cheap insurance.** Establish business line of credit BEFORE you need it (banks lend to businesses that don't need money). Provides liquidity buffer for unexpected gaps.

11. **Cash flow shocks compound.** Lost major customer + delayed payment from another + unexpected expense = cash crisis even from modest individual events. Reserves protect against compound scenarios.

12. **Forecast monthly, review weekly during stress.** Annual forecasts are insufficient. Monthly forecasts standard. Weekly during cash-tight periods. Forecast vs. actual variance reveals problems early.

Common mistakes to avoid

Confusing profit with cash flow. Profitable businesses can fail from poor cash management; profit ≠ cash.
Insufficient cash reserves. Aim for 3-6 months operating expenses (established) or 12-18 months runway (startup).
Optimistic revenue projections. Use conservative growth assumptions; surprise upside is welcome, surprise downside is fatal.
Ignoring receivables aging. 30-day vs. 90-day customer payment terms can swing cash position by hundreds of thousands of dollars.
Not separating personal and business cash. Creates tax problems and obscures true business performance.
Waiting until cash crisis to seek financing. Banks lend to businesses that don't need money; establish credit lines before you need them.

Frequently Asked Questions

Sources & further reading

Small Business Financial Management — U.S. Small Business Administration
Cash Flow Management Resources — SCORE Foundation
Business Financial Statement Standards — Financial Accounting Standards Board

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Cash Flow Calculator

Inputs

Monthly Revenue

Annual Revenue Growth

Cost of Goods Sold

Operating Expenses

Payroll & Benefits

Loan/Debt Payments

Effective Tax Rate

Current Cash on Hand

Projection Period (Months)

Results

Monthly Net Cash Flow

$3,200

Cash Flow Margin

12.8%

Monthly Surplus

$3,200

Projected Cash (12mo)

$95,751

Monthly Projection

Month	Revenue	Expenses	Net Cash Flow	Cash Balance
1	$25,000.00	$21,800.00	$3,200.00	$53,200.00
2	$25,199.35	$21,890.91	$3,308.45	$56,508.45
3	$25,400.30	$21,982.54	$3,417.76	$59,926.21
4	$25,602.84	$22,074.90	$3,527.95	$63,454.16
5	$25,807.00	$22,167.99	$3,639.01	$67,093.17
6	$26,012.79	$22,261.83	$3,750.96	$70,844.12
7	$26,220.22	$22,356.42	$3,863.80	$74,707.92
8	$26,429.30	$22,451.76	$3,977.54	$78,685.47
9	$26,640.06	$22,547.87	$4,092.19	$82,777.66
10	$26,852.49	$22,644.73	$4,207.75	$86,985.41
11	$27,066.61	$22,742.38	$4,324.24	$91,309.65
12	$27,282.45	$22,840.80	$4,441.65	$95,751.30

Last updated: July 28, 2026Reviewed by the CalcMountain editorial team

About this calculator

Formula

How to use this calculator

Enter current monthly revenue (last month's revenue is typical starting point).
Enter expected annual revenue growth rate. Use 0% if you're uncertain — conservative is better than optimistic for cash projection.
Enter COGS (cost of goods sold / direct production costs).
Enter operating expenses (rent, utilities, software, marketing, etc.).
Enter payroll and benefits separately (largest expense for most small businesses).
Enter loan/debt service payments.
Enter effective tax rate (corporate or pass-through; consult accountant).
Enter current cash on hand.
Select projection period (12 months for typical planning; 6 months for short-term cash crunch analysis; 18-24 months for longer-term planning).
Review monthly cash flow, cumulative cash position, and runway projection.
Stress test by entering pessimistic scenarios: revenue 20% lower, expenses 10% higher. Does the business survive?
For startups: aim for 12-18 months runway as buffer against unexpected challenges.
For established businesses: maintain 3-6 months operating cash as reserve.
Update projection monthly — actual results vs. projection reveals forecast accuracy and emerging issues early.