These three numbers get thrown around a lot — but they’re not interchangeable

You’re in a board meeting or talking to investors and someone asks:

“What’s your burn right now?”
“How much runway do you have?”
“How’s cash flow looking?”

They sound similar — and they’re often bundled together. But they mean different things, and as a founder, knowing which to focus on (and when) can mean the difference between a smart growth decision and a finance-induced panic spiral.

So let’s break it down. What each one means, how they work together, and which one deserves your attention right now.

Burn rate: how fast you’re losing cash

This is the one most founders are familiar with. Burn rate is the amount of cash you’re spending each month, usually shown as:

• Gross burn: all your outgoing cash (total expenses)
• Net burn: expenses minus revenue (how much cash you’re actually down per month)

For example:

• You’re spending £120k/month
• You’re bringing in £40k/month
• Your net burn is £80k/month

Burn rate is useful because it tells you how “hot” the engine is running — how quickly you’re consuming capital. But it’s just a speedometer. It doesn’t tell you how far you can go.

That’s where runway comes in.

Runway: how long you’ve got left at your current burn rate

This is your time horizon. Runway = Cash in the bank ÷ Net Burn.

Using the example above:

• You’ve got £400k in the bank
• Your net burn is £80k/month
• You’ve got 5 months of runway

It’s simple, but crucial. Runway tells you how long you can keep going before you need to raise, cut spend, or hit profitability.

But — and this is important — runway is only as reliable as your forecast. If your costs spike unexpectedly or revenue drops, that 5 months could shrink fast. That’s why burn rate and runway should always be reviewed together.

And then there’s the third piece: cash flow.

Cash flow: what’s actually happening in your bank account

Cash flow tracks the timing of money coming in and out — not just how much, but when.

Here’s why that matters:

• You close a big deal, but the client pays in 60 days
• You hire someone new, and their salary starts immediately
• You pay annual software bills up front

So even if your burn rate is stable and your runway looks healthy, poor cash flow can still cause serious short-term stress — like struggling to make payroll even though your accounts say you’re “fine.”

Cash flow is the real-time pulse. It shows you what’s going on now — not what’s theoretically happening over 12 months.

So… which one should you obsess over?

The honest answer? All three — but at different times and for different decisions.

Focus on burn rate when:

• You’re scaling and want to understand the cost of growth
• You’re hiring and want to see the impact on monthly outgoings
• You’re prepping for a raise and need to show capital efficiency

Focus on runway when:

• You’re planning your next raise and want to know your timeline
• You’re evaluating a “cut vs raise” decision
• You’re stress-testing different revenue or cost scenarios
  

Focus on cash flow when:

• You’re managing payments, payroll, or timing-sensitive costs
• You’re trying to avoid a short-term cash crunch
• You’re scaling and want to smooth out lumpy revenue or late payers

Each metric gives you a different lens. Together, they help you make grounded, confident decisions — not just gut calls or reactive moves.

What investors want to see

Most early-stage investors understand burn. They’ll ask about it regularly. But as you scale, they also want to see:

• A clear view of runway — and how you’ll extend it
• Smart cash flow planning (not just hoping invoices land on time)
• That you’re using capital wisely — not burning cash without milestones

Even if your numbers are tight, being in control of them builds trust. It shows you’re not just building product — you’re building a real business.

Visibility beats obsession

You don’t need to panic over every transaction or build a perfect model from day one. But you do need visibility.

Because once you understand how burn, runway, and cash flow connect, you can:

• Hire at the right time
• Raise with confidence
• Sleep a little easier