Burn Rate & Runway Sensitivity Simulator

Formula

Runway = Cash / Monthly Burn; Monthly Burn = Expenses - Revenue; Burn Multiple = Net Burn / Net New ARR; Break-even = month when Revenue ≥ Expenses

Runway calculation divides available cash by net monthly burn (expenses minus revenue), yielding months until cash exhaustion. Burn multiple divides net burn by net new recurring revenue added, measuring growth efficiency—how much cash is burned per dollar of sustainable revenue growth. Break-even month is when revenue growth curve intersects expense curve. These formulas work because they translate cash dynamics into actionable time horizons, efficiency metrics, and milestone targets that drive decision-making.

Worked Examples

Example 1: Pre-Revenue Startup Crisis

Problem:Startup has $800K cash, $0 revenue, burning $120K/month (15 people × $8K loaded cost). No revenue growth yet. How long until broke?

Solution:Current State: Cash: $800,000 Monthly revenue: $0 Monthly expenses: $120,000 Monthly burn: $120,000 Current Runway: $800K / $120K = 6.67 months This is CRITICAL territory. Projection (no revenue change): Month 0: $800K Month 1: $680K Month 2: $560K Month 3: $440K Month 4: $320K Month 5: $200K Month 6: $80K Month 7: -$40K (BROKE) Options: 1. Cut burn to extend runway: Cut 5 people: $40K/month savings New burn: $80K/month New runway: $800K / $80K = 10 months 2. Raise emergency bridge: $500K bridge extends by 4 months Buys time to hit milestones 3. Generate revenue quickly: Need $30K revenue ASAP to buy time Consulting, services, anything cash-positive Recommendation: Combination: - Cut burn by 25% ($30K/month) - Generate $20K/month services revenue - New

Result:6.7 months runway (CRITICAL) | Must cut burn OR raise OR generate revenue | Combination approach best

Example 2: Growth-Stage Burn Analysis

Problem:SaaS company: $5M cash, $400K MRR, $600K monthly expenses, 10% revenue growth, 8% expense growth. Analyze runway and break-even path.

Solution:Current State: Cash: $5,000,000 Revenue: $400,000/month Expenses: $600,000/month Burn: $200,000/month Current Runway: $5M / $200K = 25 months Projection with Growth: Month 0: Rev: $400K, Exp: $600K, Burn: $200K, Cash: $5M Month 6: Rev: $400K × 1.10^6 = $709K Exp: $600K × 1.08^6 = $952K Burn: $243K Cash: $5M - (cumulative burn) ≈ $3.7M Month 12: Rev: $400K × 1.10^12 = $1,256K Exp: $600K × 1.08^12 = $1,509K Burn: $253K Cash: $5M - (cumulative) ≈ $2.1M Problem: Burn is INCREASING! Revenue growing 10% Expenses growing 8% But starting from higher base ($600K vs $400K) Break-even analysis: Revenue needs to catch expenses. Revenue growing faster (10% vs 8%) Month when Rev = Exp: $400K × 1.10^n = $600K × 1.08^n 1.10^n / 1.08^n = 1.5 (1.10/1.08)^n = 1.5 1.0185^n = 1.5 n = ln(1.5) / ln(1.018

Result:25 months runway | Break-even month 22 | Should reach profitability | Monitor trajectory

Example 3: Expense Cut Scenario Planning

Problem:Startup: $1.2M cash, $50K revenue, $180K burn. Board asks for scenarios: 10% expense cut, 20% cut, 30% cut. What's the impact?

Solution:Base Case: Cash: $1,200,000 Revenue: $50,000 Expenses: $230,000 (revenue + burn) Burn: $180,000 Runway: $1.2M / $180K = 6.67 months Scenario Analysis: 10% Expense Cut: Expenses: $230K × 0.90 = $207K Burn: $207K - $50K = $157K Runway: $1.2M / $157K = 7.64 months Gain: +0.97 months 20% Expense Cut: Expenses: $230K × 0.80 = $184K Burn: $184K - $50K = $134K Runway: $1.2M / $134K = 8.96 months Gain: +2.29 months 30% Expense Cut: Expenses: $230K × 0.70 = $161K Burn: $161K - $50K = $111K Runway: $1.2M / $111K = 10.81 months Gain: +4.14 months Impact Summary: 10% cut = +1 month runway 20% cut = +2.3 months 30% cut = +4.1 months Non-linear: Each cut has bigger marginal impact. 30% Cut Details: Likely means: - Cut 6-7 people (out of ~15-20) - Eliminate contractors - Reduce cloud spend - Cut a

Result:Base: 6.7 months | 20% cut: 9 months (+2.3) | 30% cut: 10.8 months (+4.1) | Non-linear impact

Frequently Asked Questions

What is burn rate?

Burn rate is how much cash a company spends monthly beyond what it earns. If revenue is $100K and expenses are $300K, burn rate is $200K/month. Startups track burn rate obsessively as it determines survival time.

What is runway?

Runway is how long a company can operate before running out of cash, calculated as Cash ÷ Monthly Burn. With $2M cash and $200K burn, runway is 10 months. It's the most critical startup survival metric.

How much runway should a startup have?

Rule of thumb: 12-18 months minimum. Less than 12 months means immediate fundraising. Less than 6 months is crisis mode. Raising new funding typically takes 3-6 months, so start when 9-12 months remain.

What's a healthy burn multiple?

Burn multiple = Net Burn ÷ Net New ARR. Under 1.5x is excellent (efficient growth). 1.5-3x is good. Above 3x is concerning—burning too much per dollar of growth. Top SaaS companies achieve <1.5x.

Should I reduce burn or increase revenue?

Depends on stage. Pre-product/market fit: burning for growth may be premature; find fit first. Post-PMF: burn to grow is justified if unit economics work. Always easier to cut costs than grow revenue quickly.

What if revenue is growing but so are expenses?

If revenue grows faster than expenses, you're improving (burn decreasing). If expenses grow faster, you're deteriorating (burn increasing). The key is: are you approaching break-even or moving away?

How do I extend runway without raising capital?

Options: cut discretionary expenses, reduce headcount, renegotiate vendor contracts, delay non-critical initiatives, increase prices, accelerate collections, or sell assets. Emergency measures include: founder salary cuts or bridge loans.

What's the 'default dead' vs 'default alive' concept?

Default alive means your trajectory reaches cash-flow positive before runway ends. Default dead means you'll run out before reaching profitability. Most startups are default dead—they must raise or pivot to survive.

How accurate are runway projections?

Highly uncertain! Revenue growth rarely matches optimistic projections. Unexpected expenses appear. Use conservative assumptions. Scenario analysis (best/base/worst case) provides better picture than single number.

Background & Theory

Burn rate and runway analysis models cash consumption dynamics, enabling startups to make informed decisions about growth investments, expense management, and fundraising timing. ## Concept Overview Burn rate measures monthly cash outflow. Gross burn is total expenses; net burn is expenses minus revenue. Runway divides available cash by burn to find months of operation remaining. These simple metrics govern startup survival. Sensitivity analysis explores "what if" scenarios: what if revenue grows 10% faster? What if expenses increase 20%? This reveals fragility—some startups have narrow paths to success; others have wide margins for error. The growth/burn trade-off is central. Burning $500K/month to grow $100K MRR monthly might be great (5x burn multiple) or terrible (depending on unit economics and market size). Context determines whether burn is investment or waste. ## Key Variables & Intuition • **Cash on hand** — Oxygen supply; how much remains • **Monthly burn** — Oxygen consumption rate • **Revenue growth** — Improves burn by increasing income • **Expense growth** — Worsens burn; often underestimated • **Break-even path** — Month when revenue exceeds expenses ## Assumptions • Cash is accessible (not restricted) • Revenue and expense growth rates are achievable • No one-time windfalls or exceptional expenses • Company continues operating (no shutdown) • Market conditions remain stable ## Limitations & Edge Cases • **Fundraising changes everything** — New capital resets runway entirely • **Revenue acceleration** — Can improve faster than linear projections • **Expense step functions** — Hiring 10 people at once spikes burn • **Seasonal variations** — Q4 may differ from Q1 • **One-time costs** — Office build-out, legal fees distort monthly burn **Scenario:** Company has 8 months runway, assumes 3 months to close funding. Raise takes 7 months due to market conditions. Runway exhausted before close. Emergency bridge financing at bad terms or shutdown. ## Interpretation Guide Runway under 6 months is crisis—raise or cut immediately. 6-12 months is caution—start fundraising. 12-18 months is healthy—focus on metrics. 18+ months is comfortable—optimize for growth. Burn multiple under 1.5x enables aggressive growth. 1.5-3x is acceptable. Above 3x requires justification (capturing massive market, defending against competitor, etc.). ## Practical Tips • **Project conservatively** — Revenue will grow slower; expenses faster than hoped • **Model scenarios** — Best, base, worst case at minimum • **Track weekly** — Monthly reviews miss problems developing • **Plan cuts in advance** — Know what you'd cut at 12, 9, 6 months • **Communicate to team** — Transparency builds trust for tough decisions • **Build buffer** — Unexpected always happens; hold back 15% • **Start fundraising early** — At 12 months, not 6 • **Monitor burn trends** — Increasing burn while revenue flat is danger sign ## Common Mistakes • **Overly optimistic revenue growth** — "We'll triple next quarter!" Usually doesn't happen • **Forgetting expense growth** — Headcount, vendors, infrastructure all increase • **Ignoring one-time costs** — Lawsuit, office move, compliance shock the model • **Not stress testing** — What if everything is 30% worse than planned? • **Assuming funding is certain** — Markets close; always have Plan B • **Waiting too long to cut** — Earlier cuts extend runway more ## When NOT to Use • **For profitable companies** — Runway is infinite; focus on growth efficiency • **Immediately post-raise** — Freshly capitalized, focus on execution • **During fundraise** — You're already addressing the problem

History

Burn rate and runway analysis became central to startup finance as venture-backed business models normalized burning capital to achieve growth, requiring sophisticated cash management frameworks. ## Origins & Why It Emerged Early startups (pre-1990s) were typically bootstrapped, making profitability an immediate necessity. The venture capital model changed this—companies could operate at losses while pursuing growth, betting future revenue would justify current losses. The dot-com boom (1995-2000) saw extreme burn rates. Companies spent wildly on customer acquisition, brand building, and infrastructure, betting on "get big fast" strategies. When the bubble burst, thousands of companies with 18+ months of runway went bankrupt as funding dried up instantly. The post-crash era (2001-2005) brought discipline. "Default alive" became the goal—path to profitability with existing cash. Burn rate awareness replaced growth-at-all-costs mentality. ## How It Evolved in Practice Y Combinator and Paul Graham popularized "default alive vs default dead" analysis in 2015. The simple question—will you reach profitability before running out of money?—clarified strategic positioning. Most startups are default dead, requiring additional funding. The 2010s SaaS boom introduced burn multiple (burn ÷ new ARR) as an efficiency metric. Companies could burn aggressively if each dollar burned generated significant revenue growth. This nuanced the conversation from "burn is bad" to "burn efficiently." Scenario planning became standard. CFOs model multiple runways: base case, revenue miss, expense overrun. Sensitivity analysis shows which variables matter most—often headcount dominates. ## Modern Usage Today Modern startups track burn weekly, project runway monthly, and update scenarios quarterly. Dashboard culture makes burn rate as visible as revenue. Boards review burn and runway every meeting. The 2022-2023 funding slowdown revived burn discipline. "Extend your runway" became universal advice. Companies cut burn 20-40% to reach profitability or extend runway 18+ months. The playbook: hiring freeze, contractor cuts, reduce cloud spend, and kill low-ROI initiatives. Burn rate now segments by department—engineering burn, sales burn, marketing burn. This granularity enables precise cuts targeting lowest-ROI spend. ## Common Misconceptions Historically • **"Burn rate is just expenses"** — It's expenses minus revenue; revenue growth improves burn • **"More runway is always better"** — Beyond 18-24 months, incremental runway adds little safety • **"Cutting burn means failure"** — Discipline and efficiency often improve company health • **"Break-even means success"** — Profitability at tiny scale may not create valuable business • **"You can always raise more"** — Funding environments change; assume this is your last raise