Startup runway is the number of months your company can keep operating before its cash runs out, worked out by dividing your cash balance by your monthly net burn. Simple on paper. Easy to get wrong in practice.
Get it wrong and you'll either raise too late or spend too cautiously. This guide covers what startup runway means, how to calculate it from real cash, the mistakes that distort it, the UK payment dates that catch founders out, and why investors press on this number.
What Is a Startup Runway?
Startup runway is the length of time a company can operate before it runs out of cash, assuming spending stays at current levels. The formula is cash balance divided by monthly net burn (Corporate Finance Institute).
Here is a worked example using the same figures as Corporate Finance Institute's, shown in pounds. A startup holds £250,000, spends £90,000 a month and brings in £20,000. Net burn is £70,000, so runway is about 3.6 months.
Runway is measured in months because monthly spend is how founders plan: payroll, rent, software, tax. It tells you how long you have to hit your next milestone or raise again.
Burn Rate vs Runway
Burn rate measures how fast you spend cash each month, while runway measures how many months that cash will last. One is speed, the other is time.
When people compare burn rate vs runway, the key split is gross and net burn. Gross burn is your total monthly cash outflow. Net burn is gross burn minus the cash you actually receive from customers. Runway uses net burn.
Using the wrong one changes the answer dramatically. Take a company with £4.5m in cash and £520,000 of gross burn. It appears to have 8.7 months. On net burn of £300,000, the same company has 15.0 months. That's a gap of 6.3 months from one wrong input (illustration based on an Indinero example).
Burn multiple is a separate measure. David Sacks of Craft Ventures introduced it in April 2020: net burn divided by net new annual recurring revenue. In his example, burning £2m in a quarter while adding £1m of ARR is a 2x multiple, which he calls reasonable for an early-stage startup. Burning £5m for the same £1m is 5x, which he calls terrible (Craft Ventures, figures shown in pounds). It suits software-as-a-service businesses. It says little about a company without recurring revenue.
Cash Runway vs Startup Runway
Cash runway and startup runway mean the same thing: months of cash left at your current net burn. Allianz Trade notes that in conversations with investors or advisers, "runway" almost always means cash runway tied to burn rate.
So don't worry about the label. Worry about the inputs. When you quote your cash runway to anyone, state three things together: your cash balance, your net burn, and the resulting months. It removes ambiguity and shows you know your numbers.
How to Calculate Startup Runway Step by Step
To calculate startup runway, divide the cash in your bank by your average monthly net burn over at least the last three months. Work from bank statements, not your profit and loss.
If you're wondering how to calculate startup runway properly, follow this sequence:
- Reconcile first: Match your bank statement to your accounting records so the cash figure is right.
- Total your monthly outflows: That's your gross burn.
- Subtract cash actually received: Count payments that landed, not invoices you've raised.
- Average at least three month: This smooths out lumpy months.
- Divide cash by that net burn: The answer is your months of runway.
A quick cross-check: true burn is the month-on-month change in your bank balance, excluding money raised from investors. If that disagrees with your accounts, the gap sits in timing differences. Find it early.
The simple formula assumes spending stays flat. If you're hiring, a month-by-month cash forecast gives a truer picture.
Common Runway Calculation Mistakes
The most common runway mistakes are counting invoices instead of cash received, including funding you haven't banked, and letting one unusual month skew your burn.
Payroll timing matters too. Three payrolls can land in two months of the year, which in one Indinero example turns a £300,000 net burn month into £455,000 with nothing operational having changed. Treat one odd month as noise, not a trend.
UK-Specific Cash Timing Traps
UK founders face recurring HMRC payments that hit cash on fixed dates: PAYE, VAT and Corporation Tax, plus changes to R&D tax relief. Know the dates before they land.
- PAYE and employer National Insurance are due by the 22nd of the following tax month, or the 19th if you pay by cheque (GOV.UK). Tax months run from the 6th to the 5th.
- VAT returns and payment are due one calendar month and seven days after the end of your accounting period, even if that date falls on a weekend or bank holiday (GOV.UK).
- Corporation Tax is due nine months and one day after your accounting period ends (GOV.UK). That's earlier than the Company Tax Return, which is due 12 months after the period end.
- R&D tax relief changed for accounting periods beginning on or after 1 April 2024, when the merged R&D expenditure credit scheme replaced the old RDEC and SME schemes (GOV.UK). Claims need an Additional Information Form or they're invalid (HMRC guidance, GOV.UK).
Build these dates into your forecast so they never surprise your runway. We haven't quoted a payout time for R&D claims, because we couldn't confirm a reliable official figure. Check HMRC's current guidance before you count R&D money as coming in.
Why Investors Probe Your Runway
Investors probe your startup runway because it shows how much time you have to prove your next milestone, and how much pressure you're under when you ask for money. CRV describes it as "the budget a founder has to prove the next milestone."
Timing is the practical concern. CRV puts the median gap between seed close and Series A close at roughly 20 to 25 months, with some analysis suggesting founders plan for about 24 to 30 months of runway from seed (CRV, 2026). JPMorgan's 2020 analysis adds that investors generally look more cautiously at companies with less than six months left.
Benchmarks vary by stage, source and market, so treat any single number with care. What doesn't vary is the principle: know your figure, and know what it assumes.
Paul Graham's 2015 Y Combinator essay frames the underlying question. Will you reach profitability on the money you have left, if expenses stay constant and revenue keeps growing at its recent pace? If yes, you're "default alive". If not, "default dead" (Y Combinator).
How to Keep Your Runway Number Accurate
Keep your runway accurate by recalculating it every month from bank data and reconciling it against your accounts. Keep a rolling 13-week cash flow forecast alongside it, so you see problems before they arrive.
Start raising earlier than feels necessary. JPMorgan's 2020 analysis notes that investors are more cautious with companies below six months of runway, and CRV's figures show how long the gap between rounds can run. Building in time protects your negotiating position.
Recalculate sooner if something big changes: a new hire, a lost customer, a pricing shift. The number you calculated last quarter describes a company that no longer exists.
FAQs
1. How much runway should a startup have?
There's no single answer, because benchmarks depend on stage, market and source. CRV's 2026 analysis suggests planning for 24 to 30 months from seed, given the 20 to 25 month median gap to Series A. Older guidance cites shorter periods, so anchor your target to your next milestone, not a fixed number.
2. What is a good burn multiple?
A lower burn multiple means more efficient growth. In Craft Ventures' essay, David Sacks calls 2x reasonable for an early-stage startup and 5x terrible. It's a software-as-a-service metric based on net new ARR, so it may not suit businesses without recurring revenue.
3. How many months of runway do investors want?
There's no fixed rule, but more is safer. CRV suggests planning for roughly 24 to 30 months from seed, while JPMorgan notes investors are more cautious below six months (2020).
Also read: What UK Founders Need to Know About the Redundancy Process for Employers
Sources: Corporate Finance Institute; GOV.UK (Pay employers' PAYE; Sending a VAT Return; Pay your Corporation Tax bill; R&D tax relief: the merged scheme and enhanced R&D intensive support); HMRC guidance on GOV.UK (CIRD181000); Craft Ventures ("The Burn Multiple", April 2020); CRV (2026); JPMorgan (2020); Y Combinator; Allianz Trade; Indinero. Figures reflect the most recent available data at the time of writing.
The EP+ Editorial Desk covers UK startups, founder stories, and venture capital. All editorial content is independently produced and human-reviewed before publication.
