Cash flow vs profit: the difference that catches every founder out

It's one of the more brutal surprises in business ownership: the numbers say you made a profit, and yet there's no money in the account to pay the bills. It's not a contradiction. It's the difference between profit and cash, and it trips up experienced founders as often as first-timers.

Profit is what's left once you subtract costs from revenue on paper, whenever that revenue and those costs are recognised. Cash is what's actually sitting in the bank right now. A business can be profitable and still be cash-poor if money owed to it hasn't arrived yet, while money it owes has already gone out.

Where the gap usually comes from

The most common culprit is timing: you deliver the work or the product now, invoice thirty days later, and the client pays thirty days after that — while your own costs, wages and supplier bills didn't wait around for any of it. Stock is another classic one: cash tied up sitting on a shelf is cash that isn't in the bank, even though it'll eventually count as profit when it sells.

Growth makes this worse before it makes it better, which is the part that catches founders most off guard. A business that doubles its order book also roughly doubles the gap between paying for materials and labour up front and collecting payment weeks later. Rapid, profitable growth is one of the most common causes of a cash crunch — not because the business is doing badly, but because it's doing well faster than the cash cycle can keep up with.

Profit is an opinion. Cash is a fact.

Why 'profit is an opinion' isn't just a soundbite

Profit depends on judgement calls — how you value stock, when you recognise revenue on a long project, how you depreciate an asset. Change a reasonable assumption and the profit figure moves, sometimes significantly, without a single pound actually changing hands differently. Cash doesn't have that flexibility. There either is or isn't money in the account to cover Friday's payroll, and no accounting judgement changes that answer.

A worked example

Imagine a business that completes £50,000 of work in a month, all invoiced on thirty-day terms, while paying £30,000 in wages and supplier bills as they fall due that same month. On paper, that month shows a healthy £20,000 profit. In the bank, it shows £30,000 leaving and nothing yet arriving — a cash shortfall in a month that was, by every accounting measure, a good one. The profit is real. It's also thirty days away, and the wages aren't.

What to actually track

A profit and loss statement, checked monthly, tells you whether the business model works. A rolling cash flow forecast — even a simple one, thirteen weeks out — tells you whether you'll still be able to pay everyone in the meantime. Most small businesses have the first and skip the second, which is exactly backwards for spotting trouble early.

A thirteen-week forecast doesn't need to be sophisticated to be useful. List what's actually due in and out, week by week, based on real invoices and known bills rather than averages. Update it weekly rather than building it once and letting it go stale. The value isn't in perfect accuracy months out — it's in seeing a tight week coming with enough runway to actually do something about it, whether that's chasing an invoice early or delaying a non-urgent purchase.

Financing tools worth knowing about

When the timing gap genuinely can't be closed by chasing payment faster, there are established ways to bridge it rather than simply hoping. Invoice finance — factoring or discounting — lets you draw down a percentage of an invoice's value as soon as it's raised, rather than waiting for the customer's payment terms to run their course. It comes at a cost, and works best used deliberately for a real, provable timing gap rather than as a permanent crutch for a business that's actually just underpriced.

A business overdraft or revolving credit facility, agreed in advance while the business looks healthy rather than requested in a panic when it doesn't, is worth having in place before you need it. Lenders are far more receptive to a facility request from a business that clearly isn't currently desperate — arranging the safety net is a job for a calm month, not a crisis one.

The tax lump that catches profitable businesses out

Corporation Tax and VAT are particular culprits here because they arrive as lump sums, months after the profit or the sales that generated them — by which point the cash has often already been spent on wages, stock or growth that felt perfectly affordable at the time. Setting aside your Corporation Tax and VAT liabilities into a separate account as you go, rather than treating whatever's sitting in the current account as spendable, turns a nasty quarterly surprise into a bill you already knew was coming.

Warning signs worth watching for

A few patterns are worth treating as an early warning rather than a one-off blip: your average customer payment time creeping out, thirty days quietly becoming forty-five; your own supplier terms tightening as they lose patience with your payment history; or a growing reliance on one large, slow-paying customer whose invoice value is bigger than your entire cash buffer. None of these are emergencies in isolation. Together, and left unaddressed, they're exactly the pattern that turns a profitable business into a cash-flow crisis over a couple of quarters.

The levers that actually move cash

When cash is tight, most owners reach for the same lever — chase sales harder — when it's often not the fastest one available. Getting customers to pay faster (deposits, shorter payment terms, prompting invoices the day they're due rather than a week after) usually moves the needle faster than winning new business, because the cash from new business still has to travel through the same slow payment cycle before it lands.

If there's one habit worth building this month, it's this: don't just look at what you made. Look at when the money for it actually lands, and build your plans around that date, not the invoice date.

Common questions

How do I build a 13-week cash flow forecast?

Open a spreadsheet with 13 columns, one per week, and start with today's actual bank balance. Row by row, list money coming in — real invoices, against the week you genuinely expect payment rather than the week your terms say it is due — and money going out: payroll, rent, VAT, supplier bills, loan repayments, your own drawings. Each week's closing balance becomes the next week's opening one. Then look for the week the line goes red. That, not the total at the end, is the output you are after. Update it every Friday with what actually happened, because a forecast built once and left alone stops being true within a fortnight. Half an hour a week maintains it.

How much cash should my business keep in reserve?

Three months of fixed costs is the standard working answer — rent, payroll, insurance, software, loan repayments, everything that leaves the account whether or not you sell anything that month. Add up one month of those and multiply by three; that is your target buffer. Businesses with lumpy income or long payment cycles need more, and a business paid on the day of sale needs less. Keep it in a separate account rather than the current account, because money you can see is money you spend. And arrange any overdraft or credit facility in a calm month: lenders are far more receptive to a business that clearly is not currently desperate.

Can I charge interest when customers pay late?

Yes, automatically, under the Late Payment of Commercial Debts (Interest) Act 1998 — the right exists whether or not your contract mentions it. Statutory interest runs at 8% above the Bank of England base rate, which at the current 3.75% makes 11.75% simple interest on the overdue amount, running from the day payment fell due. You can also claim fixed compensation on top: £40 on debts under £1,000, £70 on debts between £1,000 and £10,000, and £100 on debts of £10,000 or more. This applies between businesses, not to consumers. Most suppliers never invoke it, but knowing you are entitled to changes the tone of a chasing call considerably.

How much should I set aside for Corporation Tax and VAT?

Move the money the day it arises, into a separate account you do not hold a card for. For VAT, set aside the VAT element of every sale as it lands, because it was never yours to spend. For Corporation Tax, reserve 19% of profit if you expect to stay under £50,000 and 25% if you will be over £250,000; between those figures marginal relief applies and the effective rate on the band is 26.5%, so 25% is a safe reserve. The deadlines are what catch people out rather than the rates. Corporation Tax is due nine months and one day after your year end, and each VAT return and payment one month and seven days after the quarter ends.

What do I do if I genuinely cannot pay a tax bill?

Call HMRC before the deadline rather than after it — that single decision changes the outcome more than anything else you can do. HMRC's Time to Pay service can spread a bill over monthly instalments, and it is granted far more readily to someone who rings in advance with a realistic proposal than to someone who has already defaulted and stopped answering the phone. Interest still runs at the current 7.75% late payment rate on what is outstanding, but penalties can often be avoided. Have your figures ready: what you owe, what you can pay today, and what you can genuinely afford monthly. Ignoring it is the expensive route, because it escalates to enforcement and removes the goodwill that made an arrangement possible.