In this guide
How to calculate gross and net burn correctly Runway: what the number actually means Burn rate benchmarks by stage The burn multiple: the metric investors now care about most Six levers for extending runway When to raise: the runway rule The 13-week cash flow: your operational tool FAQHow to calculate gross and net burn correctly
Burn rate has two versions and they answer different questions. Understanding which number you are looking at — and which number your investors are asking about — matters more than most founders realise.
Gross burn rate
Gross burn rate is the total cash leaving the business each month: payroll, rent, software subscriptions, cloud infrastructure, marketing spend, professional fees, and every other operating cost paid in cash. It does not include non-cash costs like depreciation or share-based compensation.
Formula: Gross Burn = Total Cash Outflows in the Period
Gross burn tells you the size of your cost base. If you raised £2m and your gross burn is £100k/month, you have 20 months of gross runway — ignoring revenue entirely. Gross burn matters because it is the number that does not change when revenue fluctuates. It is the fixed exposure.
Net burn rate
Net burn rate is gross burn minus cash receipts from customers in the period. This is the number that actually reduces your bank balance each month.
Formula: Net Burn = Gross Burn − Cash Receipts from Customers
Important: cash receipts, not recognised revenue. If a customer pays £36k annually upfront, you receive £36k of cash in month 1 even though you will only recognise £3k/month in your P&L over the following 12 months. Annual billing dramatically improves net burn in the months of collection, which is why the billing model is one of the highest-impact cash levers available.
Which figure to use when
Report both. In your board pack, net burn is the headline figure — it is the actual reduction in your bank balance. Gross burn sits alongside it to show the underlying cost base and how it would look if revenue growth stalled. Investors asking about burn rate typically want net burn; investors stress-testing your downside scenario will look at gross burn.
The rolling average problem
Single-month burn figures are noisy. Payroll falls on different days, VAT quarters create lumpy outflows, and one large annual supplier payment can distort a single month significantly. Use a 3-month rolling average of net burn as your primary reported figure. Update it monthly and track the trend — a rising rolling average is an early warning signal that costs are growing faster than revenue.
Runway: what the number actually means
Runway is the number of months until the bank account reaches zero at current net burn. It is the most important operational metric in a cash-consuming early-stage business — and it is the metric that most founders track too infrequently and too imprecisely.
Formula: Runway (months) = Cash Balance ÷ Monthly Net Burn
But this simple formula understates the complexity. Runway at current burn assumes: the burn rate does not change; revenue growth continues at its current pace; no large one-off outflows (VAT quarters, annual insurance, debt repayments) distort future months; and the bank balance today is fully available (no minimum cash covenants, no restricted cash). All four of these assumptions can be wrong simultaneously, which is why runway must be calculated from a properly built 13-week cash flow forecast, not from a single division of bank balance by average burn.
Runway under scenarios
The single most important cash visibility tool is a three-scenario runway calculation: what is runway at current burn (base), what is runway if revenue growth is 20% below plan (downside), and what is runway if two or three key hires are made in the next 90 days (growth plan). These three numbers give the board — and the founder — a clear picture of the range of outcomes and the decisions that need to be made at different points.
Burn rate benchmarks by stage
| Stage | Typical Gross Burn | Healthy Net Burn | Minimum Runway |
|---|---|---|---|
| Pre-seed (pre-revenue) | £15k–£40k/month | £15k–£40k/month | 18 months |
| Seed (£0–£500k ARR) | £40k–£120k/month | £25k–£90k/month | 18 months |
| Series A prep (£500k–£2m ARR) | £100k–£250k/month | £50k–£180k/month | 15–18 months |
| Series A (£2m–£8m ARR) | £200k–£600k/month | £80k–£400k/month | 18–24 months |
| Series B (£8m+ ARR) | £400k–£1.5m/month | £100k–£800k/month | 18–24 months |
Ranges are illustrative. Actual burn depends on team size, office costs, go-to-market investment, and revenue billing model. Figures are approximate UK market norms as of 2026.
The burn multiple: the metric investors now care about most
The burn multiple is a measure of capital efficiency: how many pounds of net new ARR are you generating for every pound of net burn? It was popularised by David Sacks of Craft Ventures and has become one of the most cited efficiency metrics among UK and US Series A/B investors in 2024–2026.
Formula: Burn Multiple = Net Burn / Net New ARR
A burn multiple of 1.0 means you are spending £1 of net burn for every £1 of new ARR you generate. A multiple of 0.5 means you are generating £2 of ARR for every £1 burned — highly efficient. A multiple of 3.0 means you are spending £3 for every £1 of ARR — concerning.
| Burn Multiple | Signal | Investor View |
|---|---|---|
| Below 1x | Exceptional capital efficiency | Premium valuation multiple |
| 1x – 1.5x | Strong — investment generating good returns | Strong appetite to invest |
| 1.5x – 2x | Acceptable — common at high-growth stage | Acceptable with good growth |
| 2x – 3x | Concerning — requires explanation | Will probe GTM efficiency hard |
| Above 3x | Poor — capital not generating ARR efficiently | Significant valuation pressure |
The burn multiple is particularly valuable because it links the burn conversation to the growth conversation. A high burn multiple is only acceptable if growth is sufficiently strong — and it needs to be demonstrably improving as the business scales. A burn multiple that is high and flat (or rising) is a red flag that the go-to-market motion is not becoming more efficient with scale.
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Six levers for extending runway without cutting your team
When runway is shortening faster than planned, the instinct is often to cut headcount. This is sometimes the right call — but it is rarely the first call. Headcount reductions are irreversible, carry significant morale and culture costs, and often damage the growth trajectory that investors are paying for. Before going there, these six levers typically yield 3–6 months of additional runway with limited downside.
Switch monthly to annual billing
★★★★★ Very HighEvery customer who converts from monthly to annual billing sends 10–11 extra months of cash into your bank account immediately. If 30% of your customer base is on monthly billing and you convert half of them to annual, you can add 2–4 months of runway in a single quarter with zero cost reduction. Offer a meaningful discount (10–15%) to drive the conversion.
Reduce debtor days (collect faster)
★★★★ HighIf your average debtor days is 45 and you get it to 25, you recover 20 days of receivables as cash — on £500k ARR that is roughly £27k in additional cash. Automate invoice chasing, move to direct debit for renewals, and review any customers on 60-day payment terms.
Cut non-headcount discretionary spend
★★★ Medium–HighSoftware subscriptions, office costs, external agencies, travel and entertainment, and events. For most Seed-stage SaaS companies, a disciplined review finds 15–25% savings in this category without touching headcount. Build a monthly spend report and review every item above £500/month.
Pause planned hires (not existing team)
★★★★ HighA planned hire that slips by 3 months saves the fully loaded monthly cost (salary + NI + pension + equipment + software licences) for those 3 months. On a £60k salary role that is roughly £22k of gross burn avoided. If you have 6 planned hires and defer each by an average of 2 months, the saving is material.
Negotiate extended payment terms with suppliers
★★ MediumMoving key suppliers from 30-day to 60-day terms does not reduce your total outflows — but it defers them, improving your near-term cash position. Infrastructure providers, agencies, and professional service firms are often willing to extend terms for a good customer relationship.
Accelerate upsell and expansion revenue
★★★★ HighEvery pound of expansion revenue reduces net burn by a pound. A structured upsell motion targeting the top 20% of customers by ACV with an additional product or expanded seat licence can add meaningful MRR within 90 days. Expansion revenue has near-zero CAC — it is the most capital-efficient growth you can achieve.
When to raise: the runway rule
The decision about when to start a fundraising process is one of the most consequential timing decisions a founder makes. The runway rule is simple: start the fundraise when you have 18–24 months of runway remaining. The logic is equally simple.
A UK Series A fundraise takes an average of 5–8 months from first meeting to close in 2026. A realistic downside scenario is 10–12 months. If you start with 18 months of runway, you close with 6–13 months remaining — enough to operate, with a buffer. If you start with 10 months of runway, you close with zero to two months remaining — which means you are negotiating with a gun to your head. Investors know it. They will use it.
The optimal negotiating window
The best time to raise — when you have maximum negotiating leverage and can walk away from a bad term sheet — is when growth is strong, metrics are clean, and runway is comfortable. This is also the moment when most founders feel least urgency about raising. That is the paradox of fundraising timing: the best time to raise is when you feel like you do not need to.
The 13-week cash flow: your operational tool
A 13-week rolling cash flow forecast is the operational complement to the strategic runway model. Where the runway calculation gives you a directional answer (“approximately 14 months”), the 13-week forecast gives you a week-by-week view of every cash movement — payroll run dates, HMRC payment deadlines, supplier payments, and expected customer collections — over the next quarter.
It is the tool that prevents the surprises that destroy companies: discovering in week 11 that the VAT payment and the payroll run land in the same week with insufficient cash to cover both. With a 13-week forecast updated weekly, that collision is visible in week 1, when there are 12 weeks to find a solution.
What the 13-week forecast must include
- Opening cash balance each week, derived from the prior week’s closing balance
- Customer receipts by week — based on invoice due dates and expected payment patterns
- Payroll runs — on the actual payment dates, fully loaded
- HMRC payments — PAYE/NI monthly, VAT quarterly, corporation tax instalments
- Key supplier payments — cloud infrastructure, key software, agency retainers
- Any anticipated one-off outflows — legal fees, recruitment, events
- Closing cash balance each week, showing the minimum cash point in the period
The 13-week forecast is not an accounting document — it is a management tool. It should be built on expected cash movements, not accruals, and updated every week by the CFO or finance lead. If it is not being maintained weekly, it is not serving its purpose.