← Back to articles

Runway Calculation: How Many Months of Survival on Current Cash

The Runway Reality Check Every Founder Needs

Runway is the most important number you should know about your company, yet it's often the most nebulous. "We have enough cash" is not a plan. "We have 18 months of runway" is a plan. It determines when you must raise capital, when you can hire aggressively, and whether you can survive a delayed funding round. Understanding your exact runway—not an estimate, but a calculated figure—separates founders who are in control from founders who discover they're out of cash with no Plan B.

The calculation is simple. The execution and adjustments are where most founders get tripped up.

The Basic Runway Formula

Runway (months) = Cash on hand / Monthly burn

That's it. Everything else is definition and adjustment.

Example: You have $2M in the bank and burn $150K/month. Runway = $2M / $150K = 13.3 months.

Which burn to use? It depends on your question:

• Conservative runway (assumes revenue disappears): Use gross burn. Runway = $2M / $200K gross burn = 10 months. This tells you: "Even if we lose all customers tomorrow, we have 10 months to fix things or raise capital."
• Current path runway (assumes revenue stays flat): Use net burn. Runway = $2M / $100K net burn = 20 months. This tells you: "At our current revenue and burn trajectory, we have 20 months to profitability or next funding."

Most founders should track both and present the conservative runway (gross burn) to investors. It signals risk awareness.

Which Numbers to Include in "Cash on Hand"

Cash on hand sounds straightforward but has subtle adjustments:

Include:

• Checking account balance
• Savings account balance
• Money market funds or short-term investments (accessible within 1-2 days)
• Any committed capital from investors (signed but not yet funded)

Exclude:

• Accounts receivable (money customers owe you but haven't paid). Use cash basis, not accrual.
• Equipment, furniture, or other assets. They can't pay salaries.
• Credit lines or debt facilities you haven't drawn. These exist for emergency but aren't actual cash.
• Expected future funding. Until money is in the bank, don't count it.

Reserve for payroll timing: Many founders forget that payroll is monthly but sometimes happens before the full month's cash clears. If you have $2M cash, 20 employees at $7K/month average salary ($140K/month), and you pay on the 15th and end of month, you need at least 10-15 days of float to handle two payroll cycles at once. This is usually negligible, but track it if you're running tight on cash.

Example with reserves: $2M cash, but you keep $100K as a safety buffer (to handle unexpected expenses or short cash flow gaps). Effective cash for runway = $1.9M / $150K burn = 12.7 months. This is more realistic than 13.3 months because you're not planning to go to $0 cash.

The Runway Calculation in Practice: Step-by-Step

Step 1: Determine your current cash balance. Check your bank account. Today's number is what matters.

Step 2: Calculate your monthly burn (gross and net). Sum all monthly expenses (gross) and subtract monthly revenue (net). Use a 3-month rolling average to smooth spikes.

Step 3: Apply the conservative runway formula. Cash / Gross burn = conservative runway (in months).

Step 4: Apply the current-path runway formula. Cash / Net burn = current-path runway (in months).

Example:

Cash on hand: $1.5M

Gross burn: $180K/month

Net burn: $120K/month (assuming $60K revenue)

Conservative runway: $1.5M / $180K = 8.3 months

Current-path runway: $1.5M / $120K = 12.5 months

Interpretation: At current costs, you have 8.3 months before cash is depleted (worst case). If revenue stays flat, you have 12.5 months (best case, ignoring downside risks). Smart founders plan against the conservative case (8.3 months) but hope for the current-path case (12.5 months).

Runway Benchmarks by Stage

Seed stage (pre-Series A): Typical runway is 6-12 months post-seed funding. Founders plan to raise Series A before runway falls below 6 months (to avoid desperation fundraising). If you raise a $500K seed and burn $100K/month, you have 5 months of runway—you need to demonstrate Series A-readiness quickly or raise an extension.

Series A (post-fundraising): Typical runway is 18-24 months. Series A investors expect this. A 24-month runway gives you time to hit growth milestones (new ARR targets, user growth) and prepare for Series B from a position of strength. Less than 18 months and investors see risk. More than 30 months and investors see you're not spending enough to grow.

Series B (post-fundraising): Typical runway is 24-36 months. At this stage, runway is less of a constraint (you have more cash). Focus shifts to growth rate and efficiency (burn ratio). You're tracking whether you'll be profitable or need Series C before cash runs out.

Post-profitability: Runway is no longer a primary constraint. Positive cash flow means you generate cash from operations. Runway becomes a measure of how much profit you accumulate (strategic cash, not survival cash).

When Runway Becomes a Red Flag

6 months or less: You're in fundraising mode. Every day matters. You should have started Series A processes 6+ months before, so if you're at 6 months, you're behind. Expect investor pressure to show a strong current quarter before closing.

Declining runway (month-over-month): This is the worst signal. Runway should stay stable or improve. If you have 15 months one month and 13 months the next (same cash burn accelerating), you're spending cash faster than planned. Investigate why. Spikes in hiring, marketing, or other costs should be intentional.

Negative cash flow acceleration: Net burn is increasing month-over-month despite revenue growth attempts. This signals your burn is scaling faster than revenue. Red flag for Series A investors. You need to reverse this trend (reduce burn or accelerate revenue) before Series A or you'll face difficult negotiations.

Runway Extension Strategies

Reduce gross burn (immediate impact):

• Halt or reduce marketing spend (impacts future growth but saves cash immediately)
• Freeze hiring (keeps revenue team in place, pauses growth investments)
• Renegotiate vendor contracts (reduce SaaS tool spend, negotiate server costs)
• Reduce office space (move to cheaper location or remote-first)

Reducing gross burn by 20% extends runway by 25%. Example: $150K gross burn reduced to $120K extends a 10-month runway to 12.5 months. These are often emergency moves, not sustainable strategies.

Increase revenue (slower, higher-impact):

• Accelerate customer acquisition (spend more marketing to win customers faster, increasing MRR)
• Raise prices (increases revenue per customer with no proportional cost increase)
• Reduce churn (retain existing customers, increasing lifetime value)

Increasing revenue by $50K/month (net of COGS) extends runway significantly. Example: $1.5M cash, $150K gross burn, $50K revenue = 13.3 months runway. If you add $25K revenue (reducing net burn to $75K), runway extends to 20 months. Revenue growth is the best extension strategy because it's sustainable.

Raise capital: This resets the runway clock. A $3M Series A resets a 10-month runway to 20+ months (depending on spending increases with the raise).

Communicating Runway to Investors and the Board

Format (clean and simple):

"We currently have $1.5M in cash, gross monthly burn of $180K, and net monthly burn of $120K.

Current-path runway: 12.5 months (at current revenue and burn).

Conservative runway: 8.3 months (assuming revenue loss).

We're targeting Series A closure by month 10 to maintain 18-month post-raise runway."

What investors look for:

• Is your runway calculation accurate and realistic? (They'll double-check your burn math.)
• Is your fundraising timeline realistic? (If you have 8 months of runway and Series A typically takes 4-6 months, you're cutting it close.)
• Are you trending toward profitability? (Declining net burn is a positive signal.)
• Do you have contingencies if funding is delayed? (A Plan B shows maturity.)

Avoid these mistakes when presenting:

• Don't present a rosy "current-path" runway without also showing conservative runway
• Don't assume revenue growth that hasn't materialized yet (be conservative on projections)
• Don't forget to include all burn in your calculation (try to undercount marketing or hiring-related costs)
• Don't present "months of runway" without clarifying whether it's gross burn or net burn

Key Takeaways

• Runway formula: Cash on hand / Monthly burn (in months)
• Use conservative runway (gross burn) for planning, current-path (net burn) for optimism
• Seed typical: 6-12 months post-raise; Series A: 18-24 months; Series B: 24-36 months
• Below 6 months runway = fundraising urgency; declining runway = investigate and course-correct
• Revenue growth extends runway most sustainably; cost cuts are emergency measures
• Runway drives fundraising timeline: start Series A 12 months before runway expires
• Include safety buffer (10-15% of cash) to account for unexpected expenses
• Track runway monthly and communicate to board and investors transparently

Frequently Asked Questions

Should I count a line of credit or venture debt as part of cash on hand?

Not in your runway calculation. A line of credit you haven't drawn is not cash; it's an option. Only count cash actually in the bank. Venture debt you've drawn is cash (a liability on your balance sheet, but actual cash). If you're considering drawing venture debt to extend runway, model it separately as a scenario ("with $500K venture debt, runway extends to 15 months"). It's a tool, not a core assumption.

How do I account for large one-time expenses (tax payment, annual insurance) in runway?

Include them in your monthly burn calculation by spreading them across the year. Example: $60K annual tax payment = $5K/month burn impact. This creates lumpiness (actual cash goes out in Q1, not spread monthly) but smooths your runway forecast. Alternatively, model them as one-time cash events in the specific months they occur, and track runway month-by-month instead of using a simple division formula.

If my runway is declining (gross burn going up, cash stable), what should I do?

Investigate immediately. Increasing burn usually means hiring or marketing spend spikes. If you planned these spikes (hiring engineers for a growth phase), it's fine. If it's unplanned, find the source and course-correct. If it's planned, model the impact: "Runway today is 12 months, but we're hiring 5 engineers this month (adds $35K/month burn). New runway forecast is 10 months. We need revenue to scale by X to maintain runway." Be explicit about trade-offs.

Can I extend runway by delaying payments to vendors?

Technically, yes, but it's risky. Delaying a $20K vendor payment extends cash on hand by $20K for one month (extending runway slightly). But vendors will push back, relationships suffer, and critical vendors might cut you off. This is a last-resort tactic, not a strategy. If you're considering it, you're too close to zero and need emergency capital or cost cuts immediately.

What's the difference between runway and "cash available"?

Runway is cash divided by burn (measured in time). Cash available is the absolute amount. Investors care about runway because it tells them how long you'll survive; founders care about cash available because it tells them how much they have to spend. Both are important. A $2M cash balance with 20 months of runway is healthy. A $2M cash balance with 3 months of runway is a crisis.