How much runway do you need to raise? (and how to prove it)
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Raise too late and you look desperate; too early and you can't justify it. Here's how much runway looks credible to investors, and how to prove your number on demand.
The trap nobody warns you about
Here's the cruel timing of fundraising. The moment you most need money is the worst possible moment to raise it.
If you start raising with six weeks of cash left, investors can smell it. Your runway becomes their leverage. Every delay works in their favour, because they know the alternative for you is the lights going off. You're not negotiating — you're pleading.
Start too early, though, and you face a different problem: you can't really justify the raise yet, you'll dilute more than you need to, and a sharp investor will ask why you're raising now instead of proving more first.
So "how much runway do I need to raise?" is really two questions hiding in one. How much runway makes you look credible rather than desperate? And how do you prove the number, so the investor believes it?
Let's take both.
The honest answer: start at 12 months, raise by 6
There's no law here, but there's a well-worn rule of thumb that holds up across most UK seed and pre-seed rounds.
Start raising when you have around 12 months of runway left. Twelve months sounds generous when you're staring at it. It isn't. A seed round in the UK routinely takes three to six months from first conversation to money in the bank — and that's when things go well. Diligence drags, a lead pulls out, the summer happens, someone's lawyer goes quiet. Twelve months gives you room to run a proper process and walk away from a bad deal.
Treat six months as your "still credible" floor. With six months left, you can still raise from a position of relative strength. An investor sees a founder who's planned ahead, not one staring down the barrel.
Below three months is the danger zone. This is where runway stops being a fact and becomes a weakness. You can still raise — founders do it all the time — but you'll do it on worse terms, and you'll spend the whole process anxious, which shows.
The single biggest reason founders end up raising from desperation isn't a bad business. It's that they didn't know their runway early enough to start in time. They found out they had four months left in month four.
Why "credible" beats "as much as possible"
A common instinct is to raise the biggest round you can. Resist it slightly — and be ready to explain your number.
Investors don't just want to know how much you're raising. They want to know that the amount makes sense: that it buys you a clear, fundable amount of runway and gets you to a specific milestone. "We're raising £500k to give us 18 months to hit £50k monthly recurring revenue" is a sentence an investor can back. "We're raising as much as we can get" is not.
The credible founder ties the raise to runway and runway to a milestone:
- How much you're raising.
- How many months of runway that buys (the new money plus what you have, divided by your burn).
- What you'll have proved by the time it runs low — the milestone that makes the next round raisable.
That last point is the one founders forget. The job of this round isn't to survive. It's to reach the proof point that lets you raise the next one before that runway gets scary. Runway thinking doesn't stop when the money lands — it just resets the clock.
How to prove your runway (the part that builds trust)
Here's where most founders quietly lose credibility. They state a runway number in the pitch — "we've got nine months" — and then can't back it up when asked. The investor asks to see the burn behind it, and out comes a spreadsheet that's three weeks stale, or a figure that doesn't match the bank.
The moment your stated runway doesn't match your actual numbers, two things die at once: that number, and your credibility on every other number.
To prove runway, you need three things to agree:
Your cash. The real balance in the bank today — not a month-old figure. Investors will cross-check this against your bank statements in diligence, so it has to be current.
Your burn. How much you spend over what you bring in each month, averaged over the last few months so a freak cost doesn't distort it. (See: What is runway and how do I work out mine? for the plain-English version of burn and runway.)
The maths between them. Runway = cash ÷ monthly burn. One division. The investor will redo it. It needs to land on the number you said.
When those three tie together — and tie to your bank statements — your runway stops being a claim and becomes a fact. That's the difference between an investor nodding and an investor digging.
The hard way to prove it
In a spreadsheet world, proving runway is a small ordeal every single time someone asks.
You open the bank app for the cash figure. You open last month's spreadsheet for burn — except it's not reconciled, so you're not sure it's right. You redo the average. You realise the spreadsheet still has last month's one-off equipment cost in it, inflating your burn, so your runway looks shorter than it is. You patch it, send a number, and quietly hope nobody asks for the workings.
And they ask. Every investor asks. So you do this dance again next week, with a slightly different answer each time — which is exactly the inconsistency that makes an investor nervous.
The problem isn't the maths. It's that the number is reconstructed by hand each time, from records that aren't current, so it's never quite the same and never quite trusted.
How it works in Ledgers
In Ledgers, your runway is live.
Your bank feed comes in automatically and your books are continuously reconciled, so your cash figure is real and current to today — not a month-old estimate. Your burn is calculated for you from your actual spending and income, averaged sensibly so a one-off cost doesn't distort it. And your runway — cash ÷ burn — sits on screen, always current, no spreadsheet to maintain.
When an investor asks "how much runway have you got, and can you show me?", you don't reconstruct anything. You show them a number that's true today and that ties straight to the bank statements they'll see in diligence. You can model the raise too — see how many months the new money buys, against the milestone you're aiming for, with plan-vs-actual showing whether you're on track.
The number you say in the room is the number in the software is the number in the bank. That consistency is the credibility.
What you'd actually do
You're four months from your "start raising" trigger. You glance at Ledgers and see 13 months of runway — time to begin lining up conversations. You open the raise model and confirm £400k buys you 16 months at your current burn, comfortably past the revenue milestone you need for a Series A story.
In the pitch, you say "we have 13 months of runway and we're raising £400k to reach 18 months and £40k MRR." When the investor asks to see it, you pull up the live figure — cash, burn, runway — current to today and matching your bank. No spreadsheet, no stale number, no scramble.
You're raising from strength because you started in time, and you're trusted because your number proves itself.
Ready to stop reconstructing this every time someone asks? In Ledgers, your runway and burn are live — worked out automatically from your bank feed, always current, and tied to the bank statements investors will see in diligence. See your numbers without learning accounting → start free. Or try our free runway calculator → first.
New to runway? Start here: What is runway and how do I work out mine? →
Mid-raise? Next up: How to calculate and explain your burn rate to investors → and How to answer investor due diligence →
Frequently asked questions
How much runway should I have before raising?
A common rule of thumb is to start raising at around 12 months of runway and treat 6 months as the floor where you still look credible. Raising takes longer than founders expect — often 3–6 months for a UK seed round — so starting early is what keeps you negotiating from strength.
How much runway is too little to raise comfortably?
Below about three months, your runway becomes the investor's leverage rather than your plan. You can still raise, but usually on worse terms and under far more stress. The fix is to know your runway early enough to start the process before you hit that zone.
How do I prove my runway to investors?
Make three things agree: your real cash balance today, your average monthly burn, and the division between them (cash ÷ burn). They must also tie to your bank statements, because investors cross-check in diligence. A live, reconciled figure proves itself; a stale spreadsheet doesn't.
How much money should I raise?
Enough to buy a credible amount of runway — usually 18–24 months — and reach the milestone that makes your next round raisable. Investors back a specific number tied to a milestone far more readily than "as much as we can get."
See your numbers without learning accounting
Ledgers does the bookkeeping — bank feeds, VAT, year-end — and keeps your accountant in the loop. Free for pre-revenue founders.
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