How long can your startup survive?
Runway is the number that determines everything. Know your burn rate, months of cash, and what growth rate you need to reach profitability before the money runs out.
How many months of runway do I have at my current burn rate?
What is my gross burn vs net burn each month?
What are the real costs to launch this business?
At what monthly revenue do I reach break-even?
How does a new hire change my runway?
When should I start the next fundraising process?
Recommended tools
Calculators for this decision
SaaS Runway Calculator
Calculate months of runway from cash balance and burn rate.
Solves
Months of cash remaining given current cash balance and monthly net burn rate.
Startup Cost Calculator
Estimate launch costs, working capital, runway, and funding needs.
Solves
Total startup cost breakdown: one-time setup costs plus monthly operating expenses to reach runway target.
Break-even Calculator
Find break-even units and sales needed from costs and price.
Solves
Monthly revenue needed to cover all fixed and variable costs — the first profitability milestone.
Cash Flow Calculator
Calculate net cash flow from inflows, outflows, receivables, and payables.
Solves
Monthly cash in vs cash out — to spot when profit and cash diverge and plan for gaps.
Practical guide
Startup financial runway explained — and why it is the most important number
Runway is the number of months a startup can operate before it runs out of cash. It is calculated as: Current cash balance ÷ Monthly net burn rate. Net burn is gross burn (total monthly expenses) minus monthly revenue received. If you have £200,000 in the bank and your net burn is £25,000/month, you have 8 months of runway.
Most founder conversations focus on revenue growth. Investors focus on runway because it determines optionality: with 18 months of runway, you can be selective and strategic. With 4 months, you are in distress fundraising, which gets worse terms or fails. The rule of thumb for raising a round is: start 6 months before you need the money. With an 8-month runway, that means you are already fundraising — now.
The difference between gross burn and net burn matters. Gross burn is total monthly expenses regardless of revenue. Net burn is gross burn minus revenue received. Early-stage startups often confuse the two when planning. A startup with £40,000 in gross burn and £15,000 in monthly revenue has a net burn of £25,000 — but if revenue is lumpy (project-based, large contracts), net burn in some months might be much higher.
For pre-launch startups, the startup cost calculator helps model the full capital requirement: one-time setup costs (legal, equipment, branding, product build) plus the monthly operating costs until you reach break-even or raise the next round. Model three scenarios: lean (minimum viable), realistic, and full-featured. The lean scenario gives a minimum capital requirement; the realistic one is what you should raise for.
Worked example
See it in action
Scenario: Calculating runway after a seed round and planning the next fundraise
- 1Cash position: Post-seed cash: £350,000. Raised 6 months ago. Current cash: £200,000.
- 2Current burn: Gross burn: £35,000/month (payroll £22k, infrastructure £3k, marketing £5k, other £5k). Monthly recurring revenue: £8,000. Net burn: £27,000/month.
- 3Current runway: £200,000 ÷ £27,000 = 7.4 months of runway.
- 4Fundraising timeline: Need to start fundraising in approximately 1–2 months to close in 3–4 months with 3–4 months buffer remaining.
- 5Next hire impact: Adding a £4,000/month engineer increases net burn to £31,000. Runway drops to 6.5 months — making the fundraising timeline tighter.
Result
With 7.4 months of runway, this startup needs to start fundraising immediately. Adding a planned hire before securing the round reduces runway to 6.5 months and creates meaningful execution risk. The decision to hire should wait until the round is closed or the hire is demonstrably revenue-generating.
Watch out
Common mistakes to avoid
Using gross burn instead of net burn to calculate runway — overstating months of cash remaining.
Projecting revenue as linear when early-stage growth is lumpy and unpredictable.
Starting fundraising too late — less than 5 months before cash runs out means distress fundraising.
Not modelling the impact of each planned hire on runway before making the offer.
Underestimating one-time startup costs — legal, incorporation, accounting setup, and initial marketing are consistently underestimated.
Assuming break-even will happen at MRR that matches current month's expenses — as the business grows, costs often grow too.
Before you decide
Decision checklist
Do you know your current gross burn and net burn to the nearest £1,000?
Have you calculated months of runway based on current net burn (not revenue projections)?
Is your fundraising start date at least 6 months before projected cash-out?
Have you modelled runway impact for each planned hire in the next 6 months?
Have you calculated the revenue level at which you reach break-even?
Have you stress-tested runway if revenue is 25% lower than projected?
Calculated your numbers? Take the next step.
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Frequently asked questions
What is a safe amount of startup runway?
The commonly cited benchmark is 18–24 months of runway after a fundraise. This allows 6 months to execute, 6 months to see results, and 6 months to fundraise the next round with a buffer. Less than 12 months is uncomfortable. Less than 6 months is a crisis. Startups at less than 3 months of runway have limited options.
What is the difference between gross burn and net burn?
Gross burn is total monthly cash spent — payroll, infrastructure, rent, marketing, and all other expenses. Net burn is gross burn minus monthly recurring revenue received. A startup spending £40,000 and collecting £15,000 in monthly revenue has a gross burn of £40,000 and a net burn of £25,000. Runway is always calculated on net burn, not gross burn.
When should a startup start the next fundraising process?
Start when you have 6 months of runway remaining. A typical fundraising process (from first meeting to money in the bank) takes 3–5 months. Starting at 6 months leaves a 1–3 month buffer if it takes longer than expected. Starting at 3 months is distress fundraising — investors know it, which weakens your position and terms.
How do I estimate realistic startup costs?
Work backwards from launch date plus the first 6 months of operations. One-time costs: legal and incorporation, product build or initial inventory, branding and website, any capital equipment. Monthly costs: payroll, cloud/infrastructure, marketing, accounting, software tools, workspace, insurance. Add 20–30% contingency. The startup cost calculator helps structure this by category.