Your Shopify dashboard says revenue is up. Your bank balance says otherwise. That gap is the single most common problem we see with growing UK online sellers, and it almost always comes down to tracking the wrong numbers.
Revenue is not profit. Profit is not cash. And the metrics your sales platform shows you by default are rarely the ones that tell you whether the business is actually working.
This guide covers the ecommerce KPIs that matter for a UK seller, how to read them, and how monthly management accounts turn a pile of numbers into decisions you can act on. We have kept the maths simple and labelled every example clearly.
What are management accounts, and why do ecommerce sellers need them? {#what-are-management-accounts}
Management accounts are an internal financial summary you produce regularly, usually monthly, to see how the business is performing right now. They are different from your year-end statutory accounts, which look backwards and exist mainly to satisfy HMRC and Companies House.
A useful set of ecommerce management accounts typically pulls together:
- A profit and loss view for the month, with revenue, cost of goods sold, and overheads.
- A short cash-flow summary showing money in and money out.
- A handful of KPIs tracked against the previous month and the same month last year.
For online sellers this matters more than for most businesses, because your money moves through several layers before it reaches you. A sale on a marketplace passes through platform fees, payment fees, fulfilment costs, advertising, returns and VAT before it becomes profit. Your sales dashboard sees the top line. Your management accounts see what survives to the bottom.
The point is not to produce a report for its own sake. It is to spot a margin slipping, a marketing channel turning unprofitable, or stock tying up cash, while you can still do something about it.
Which profit KPIs actually matter for online sellers? {#profit-kpis}
Start with profitability, because a business can grow itself into insolvency by chasing revenue at a loss. These are the core ecommerce KPIs UK sellers should track every month.
Gross profit and gross margin. Gross profit is revenue minus the cost of goods sold (COGS), which for an online seller means the landed cost of the product itself: the unit cost, inbound shipping, and import duty. Gross margin is gross profit as a percentage of revenue. It tells you how much each pound of sales contributes before you pay to acquire the customer or run the business.
Contribution margin. This is the metric most sellers miss, and it is often the most important. Contribution margin takes gross profit and then strips out the variable selling costs that scale with each order: marketplace or platform fees, payment processing fees, fulfilment and pick-and-pack, and advertising attributable to that channel. What is left is the real contribution each sale makes towards your fixed overheads and profit. A product can have a healthy gross margin and a contribution margin near zero once fees and ad spend are in.
Net profit and net margin. Net profit is what remains after all overheads, including software, rent, salaries and your accountancy. Net margin is that as a percentage of revenue. This is the number that, over time, tells you whether the business is genuinely viable.
| KPI | How to calculate it | What it tells you |
|---|---|---|
| Gross margin | (Revenue minus COGS) / Revenue | Headroom in your pricing before selling costs |
| Contribution margin | (Gross profit minus variable selling costs) / Revenue | Whether each sale pays its own way |
| Net margin | Net profit / Revenue | Whether the whole business is profitable |
In practice, the mistake we most often see is a seller who knows their gross margin to the decimal but has never calculated contribution margin, and is quietly losing money on a bestselling product once advertising is counted.
How do I track marketing and customer KPIs? {#marketing-kpis}
Talk to an e-commerce accountant →
Marketing is usually the largest variable cost for an online seller, so a few KPIs here protect your margin directly.
Customer acquisition cost (CAC). Total marketing and advertising spend in a period, divided by the number of new customers it brought in. If CAC creeps above the contribution margin of a first order, you are paying to lose money on every new customer unless they come back.
Customer lifetime value (LTV). The total contribution margin you expect from a customer across all their orders. The relationship between LTV and CAC is what decides whether aggressive marketing is investment or waste. A common rule of thumb is that LTV should comfortably exceed CAC, but the right multiple depends on how long your cash is tied up before that lifetime value arrives.
Return on ad spend (ROAS). Revenue attributable to advertising, divided by the ad spend. Useful, but treat it with caution: ROAS is measured on revenue, not margin, so a "good" ROAS on a thin-margin product can still lose money. Always sense-check ROAS against contribution margin.
Repeat purchase rate and average order value (AOV). The share of customers who buy again, and the average value of an order. Nudging either upwards is usually cheaper than acquiring new customers, and both feed directly into LTV.
Which inventory and cash KPIs keep me solvent? {#inventory-cash-kpis}
Profit on paper does not pay suppliers. For a physical-product seller, cash is usually trapped in stock, and these KPIs tell you how efficiently.
Inventory turnover. COGS for the period divided by your average stock value. A higher number means you are selling through stock quickly rather than letting cash sit on shelves. Compare it across seasons, not just month to month.
Days inventory outstanding (DIO). Roughly how many days your average stock takes to sell. Long DIO ties up cash and raises the risk of dead stock you have to discount.
Cash conversion cycle. This pulls the picture together. It is the time between paying your supplier for stock and receiving the cash from selling it, adjusted for how quickly platforms pay you out. Marketplaces often hold your funds for days or weeks, so a seller can be profitable and still run out of cash because outflows land before payouts do.
Sell-through rate. Units sold as a percentage of units received in a period. A practical early warning for slow movers before they become a markdown problem.
If you sell across several channels, these numbers are far easier to trust when your bookkeeping is clean and reconciled to each payout. Getting reliable management accounts out of a marketplace business starts with solid bookkeeping for ecommerce businesses, because the KPIs are only as good as the data underneath them.
Illustrative example: reading one month of KPIs {#worked-example}
Illustrative example. Maya runs a UK Shopify and Amazon homeware brand as a limited company. Here is one month, simplified.
| Line | Amount |
|---|---|
| Revenue (net of VAT) | £40,000 |
| Cost of goods sold | £16,000 |
| Gross profit | £24,000 |
| Platform and payment fees | £4,000 |
| Fulfilment | £3,000 |
| Advertising | £8,000 |
| Contribution | £9,000 |
| Fixed overheads | £6,000 |
| Net profit | £3,000 |
Reading the KPIs:
- Gross margin is £24,000 / £40,000 = 60%. Healthy headroom.
- Contribution margin is £9,000 / £40,000 = 22.5%. The product pays its way, but advertising at £8,000 is eating most of the gross profit.
- Net margin is £3,000 / £40,000 = 7.5%. Profitable, but thin.
The story the numbers tell: Maya's pricing is strong, but her marketing efficiency is the constraint. If new-customer CAC is running near that 22.5% contribution, she is barely breaking even on first orders and relying entirely on repeat purchases for profit. The lever here is not price, it is advertising efficiency and repeat purchase rate, not cutting product cost.
Without contribution margin in front of her, Maya would only see a 60% gross margin and a growing top line, and conclude everything was fine.
How do VAT and tax thresholds show up in my KPIs? {#vat-tax-kpis}
A few tax facts feed directly into how you read your numbers, so build them into your management accounts rather than discovering them at year-end.
The VAT registration threshold. You must register for VAT once your VAT-taxable turnover exceeds £90,000 in any rolling 12-month period, a figure in place since 1 April 2024 (VAT registration thresholds, gov.uk). For a fast-growing seller, rolling 12-month turnover is itself a KPI worth watching, because crossing the threshold changes your pricing and your margins overnight.
Net vs gross revenue. Once registered, track revenue net of VAT in your KPIs. Mixing VAT-inclusive and VAT-exclusive figures is one of the quickest ways to misread your own margins. The standard rate is 20% (VAT rates, gov.uk).
Fees with VAT on them. Since 1 August 2024, Amazon charges UK VAT directly on its seller fees, which a VAT-registered seller reclaims as input tax. In your management accounts, record fees net of recoverable VAT so your contribution margin reflects the real cost, not the gross charge.
Making Tax Digital. If you are a sole trader, Making Tax Digital for Income Tax begins on 6 April 2026 for those with qualifying income over £50,000, extending to over £30,000 from 6 April 2027 and over £20,000 from 6 April 2028 (check when to sign up for Making Tax Digital for Income Tax, gov.uk). Keeping clean monthly records now means MTD is a non-event later.
Where your numbers start to drive bigger decisions, on registration timing, scheme choice, or how you draw profit, that is where tax advisory for ecommerce businesses earns its keep, because the right answer depends on your specific margins and growth.
How often should I review my numbers? {#review-cadence}
Monthly is the right cadence for most online sellers. It is frequent enough to catch a problem while it is small, and slow enough that the noise of day-to-day sales averages out.
Within the month, keep a light eye on the fast-moving operational figures: ad spend against ROAS, and cash against upcoming supplier payments. You do not need full management accounts weekly, but you do need to know you can pay for your next stock order.
Then, monthly, sit with the full picture: profit and margins, the marketing and customer KPIs, inventory and cash. Compare against last month and the same month last year, because ecommerce is seasonal and a month-on-month dip in January is not the same signal as one in October.
The sellers who scale calmly are not the ones with the fanciest dashboards. They are the ones who look at the same handful of honest numbers every month and act on them.
Frequently asked questions {#faqs}
What is the difference between management accounts and year-end accounts?
Management accounts are internal reports you produce regularly, usually monthly, to manage the business in real time. Year-end statutory accounts are a formal, backward-looking summary filed to meet HMRC and Companies House obligations. Management accounts help you make decisions; year-end accounts mainly satisfy compliance.
What is the single most important KPI for an ecommerce business?
There is no universal answer, but contribution margin is the one most sellers underuse and most need. It shows whether each sale actually pays its way after the variable costs of selling it, including platform fees, payment fees, fulfilment and advertising. A product can look profitable on gross margin and still lose money once those are counted.
Why is my ecommerce business profitable but always short of cash?
Usually because cash is tied up in stock and platform payouts arrive after your costs go out. You pay suppliers, advertising and fees before a marketplace releases your sales proceeds, so a profitable business can still run dry. Tracking your inventory turnover and cash conversion cycle is how you see and manage that gap.
When do I need to register for VAT as an online seller?
You must register once your VAT-taxable turnover exceeds £90,000 over any rolling 12-month period, the threshold in place since 1 April 2024. Because it is a rolling figure, a fast-growing seller can cross it mid-year, so watching rolling 12-month turnover as a KPI helps you plan for it rather than be caught out.
Do I need software to produce management accounts?
You need clean, reconciled bookkeeping more than you need any particular tool. Most cloud accounting packages can produce a basic management report once your sales channels, fees and payouts are recorded accurately. The limiting factor is almost always data quality, not the software, which is why reliable bookkeeping comes first.
Get a clear monthly view of your numbers
If your sales are growing but you are never quite sure what is left at the end of the month, the fix is a clean set of management accounts and the right KPIs in front of you. We help UK online sellers track the numbers that matter and act on them before small problems get expensive. Book a call with a Zmartly accountant through our ecommerce accounting service and we will help you build a monthly view you can actually run the business on.
