# Trading Margin, ROAS and Repeat Purchase > [ecommerce_hub_nav] Home › eCommerce Finance › Trading Margin, ROAS and Repeat Purchase THE E-COMMERCE FOUNDER'S GUIDE Trading Margin, ROAS and Repeat Purchase The easiest way to lose money in eCommerce is to look at the wrong numbers and feel reassured.… > URL: https://ascendantaccountants.com/ecommerce-finance/trading-margin-roas-and-repeat-purchase/ > Last modified: 2026-09-09T14:04:50+00:00 eCommerce Finance Menu 9 pages - [Business Model and Metrics](https://ascendantaccountants.com/ecommerce-finance/business-model-and-metrics/) - [Working Capital and Inventory](https://ascendantaccountants.com/ecommerce-finance/working-capital-and-inventory/) - [Amazon, DTC and Wholesale](https://ascendantaccountants.com/ecommerce-finance/amazon-dtc-and-wholesale/) - [Trading Margin, ROAS and Repeat Purchase](https://ascendantaccountants.com/ecommerce-finance/trading-margin-roas-and-repeat-purchase/) - [Brand-Led vs Smash-and-Grab](https://ascendantaccountants.com/ecommerce-finance/brand-led-vs-smash-and-grab/) - [Promotions, Bundles and Margin Leakage](https://ascendantaccountants.com/ecommerce-finance/promotions-bundles-and-margin-leakage/) - [Forecasting, Seasonality and Growth Pacing](https://ascendantaccountants.com/ecommerce-finance/forecasting-seasonality-and-growth-pacing/) - [Talk to an Expert](https://ascendantaccountants.com/ecommerce-finance/discover-ecommerce-finance/) - [Scaling eCommerce: Transcript](https://ascendantaccountants.com/ecommerce-finance/scaling-ecommerce-transcript/) Also in eCommerce Finance - [eCommerce Services](https://ascendantaccountants.com/ecommerce-finance/services/) [Home](/) › [eCommerce Finance](https://ascendantaccountants.com/ecommerce-finance/) › Trading Margin, ROAS and Repeat Purchase THE E-COMMERCE FOUNDER’S GUIDE # Trading Margin, ROAS and Repeat Purchase The easiest way to lose money in eCommerce is to look at the **wrong numbers** and feel reassured. These are the metrics that decide whether growth is creating value — or burning it. [Talk to an Expert  →](https://ascendantaccountants.com/ecommerce-finance/trading-margin-roas-and-repeat-purchase/#book) [Download the eCommerce Playbook  ](#playbook) Article 04  ·  10 min read    Written by Ascendant eCommerce Team ## Key Takeaways Takeaway 01 Revenue alone is a flattering lie. Trading margin tells you what is left after product cost, fulfilment and variable marketing. Takeaway 02 ROAS without context misleads. Wrong revenue base, wrong attribution, VAT-inclusive numbers — most ROAS dashboards make a weak model look healthy. Takeaway 03 The second order decides the model. Time-to-second-order and repeat rate tell you whether you have a business or an acquisition habit. E-COMMERCE HUB ### The Founder’s Guide Article 4 of 8 - [Business Model and Metrics](https://ascendantaccountants.com/ecommerce-finance/business-model-and-metrics/) - [Working Capital and Inventory](https://ascendantaccountants.com/ecommerce-finance/working-capital-and-inventory/) - [Amazon, DTC and Wholesale](https://ascendantaccountants.com/ecommerce-finance/amazon-dtc-and-wholesale/) - 04Trading Margin, ROAS and Repeat Purchase - 05[Brand-Led vs Smash-and-Grab](https://ascendantaccountants.com/ecommerce-finance/brand-led-vs-smash-and-grab/) - 06[Promotions, Bundles and Margin Leakage](https://ascendantaccountants.com/ecommerce-finance/promotions-bundles-and-margin-leakage/) - 07[Forecasting, Seasonality and Growth Pacing](https://ascendantaccountants.com/ecommerce-finance/forecasting-seasonality-and-growth-pacing/) - 08[Services](https://ascendantaccountants.com/ecommerce-finance/services/) NEED A STEER? #### 30 minutes with a finance lead — no pitch. We will tell you, honestly, where your model is leaking. [Book a Discovery Call](#book) In this article [01Why the wrong numbers deceive](#overview) [02The numbers that tell the truth](#metrics) [03Building metric clarity](#clarity) [04Trading-margin bridge](#bridge) [05Formula reference](#reference) [06FAQs](#faq) 1 The premise ## The wrong numbers will reassure you all the way to insolvency. **Revenue is not enough. ROAS on its own is not enough.** Even a healthy gross margin can flatter a weak model if paid media, shipping, returns and discounts are quietly eating the business. That is why we anchor founders around **trading margin**: the money left after the direct product cost, fulfilment drag and variable marketing spend have all had their say. ROAS, AOV, repeat purchase and time-to-second-order then explain whether trading margin is structural — or temporary. 2 The five metrics ## The numbers that tell the truth. Average order value matters because low baskets leave too little room for paid acquisition. Repeat purchase matters because that is where a weak first-order model can be rescued. Time to second order matters because a repeat six months away is much less helpful than one inside thirty days. 01Anchor metricTrading Margin Revenue − COGS − Fulfilment − Variable marketing The money left after the direct product cost, fulfilment drag and variable marketing spend have all had their say. A healthy gross margin can flatter a weak model — trading margin cannot be flattered the same way. 25–35%Target rangeWatch-outPaid media, shipping, returns and discounts quietly eat the business. Anchor founders here.02EfficiencyROAS / MER Ad revenue ÷ Ad spend  •  Total revenue ÷ Total marketing Too many dashboards use the wrong revenue base, the wrong attribution view or a VAT-inclusive number that flatters performance. Pair ROAS with MER — total revenue divided by total marketing spend. 3–5×Blended MER targetWatch-outROAS isolated by platform double-counts conversions; reach for MER.03Acquisition headroomAverage Order Value Net revenue ÷ Number of orders AOV matters because low baskets leave too little room for paid acquisition. Bundles, free-shipping thresholds and post-purchase upsells are the levers — but a discount-driven AOV is self-defeating. +15–30%Lift from bundlingWatch-outAOV propped up with discounts erodes margin faster than it lifts cash.04RetentionRepeat Purchase Rate % of customers who buy again within 90 days Repeat purchase matters because that is where a weak first-order model can be rescued. A single repeat-rate number hides cohort decay — always look at it by acquisition month. 30%+At 90 daysWatch-outReported as a single number, it hides the cohorts that never come back.05Cash velocityTime to Second Order Median days between order 1 and order 2 A repeat six months away is much less helpful than one inside thirty days. Time-to-second-order is the truest read on product–market fit because it reflects whether customers actually want the next purchase. 30–60dHealthy bandWatch-outPower-user skew. Use median, not mean. Get clearer forecasts and smarter stock decisions Book a discovery call if you want clearer forecasting, better stock decisions and more confidence in the economics of growth. [Book a Discovery Call →](https://ascendantaccountants.com/contact-us/discover) 3 The test ## A good metric stack forces clarity. Ask these four questions of any dashboard. If it cannot answer them, it is decoration. 01Are we making money on the first order? 02If not, how quickly does the second order arrive? 03What proportion of a new cohort comes back? 04How much of our customer value is real, and how much is just hope? “If a business does not know those answers, it is not scaling. **It is guessing at scale.**” That is why Ascendant pushes a **design-for-profit mindset** early. If you expect around a third of revenue to disappear into paid media, another meaningful share into product cost, more into shipping and returns, and more again into overhead, then a weak starting margin profile leaves almost nothing left to fund growth. You cannot rely on enthusiasm and headline revenue to rescue that. [RELATED GUIDE:Brand-Led vs Smash-and-Grab eCommerce— Why durable eCommerce brands earn more, longer](https://ascendantaccountants.com/ecommerce-finance/brand-led-vs-smash-and-grab/) 4 The picture ## The trading-margin bridge This is illustrative — the shape is the lesson, not the exact percentages. Where revenue actually goes before it becomes trading margin. Illustrative · Indexed to 100% of revenue Where revenue actually goes before it becomes trading margin. Illustrative · Indexed to 100% of revenue Where revenue actually goes before it becomes trading margin. Revenue100%COGS−25%Shipping & fulfilment−15%Paid media−20%Returns & discounts−10%Trading margin=30%100%Revenue−25%COGS−15%Shipping & fulfilment−20%Paid media−10%Returns & discounts=30%Trading marginPillarDeductionResult≈ 30%Of every £1 of net revenue, only about **30p reaches trading margin**. That is the pool that has to fund overhead, growth and profit — which is why a weak starting margin profile leaves almost nothing left to fund growth. 5 At a glance ## Formula reference Print this. Tape it to the wall above the dashboard. Hold every monthly review against it. MetricFormulaHealthy rangeCommon pitfallTrading marginRev − COGS − Fulfilment − Var. marketing25–35%Overhead allocated in; flatters channel mix.Gross marginRevenue − COGS60–75%Hides true unit economics. Useful, not sufficient.ROASAd revenue ÷ Ad spend (per platform)3–5×Double-counts conversions across channels.Total revenue ÷ Total marketing spend3–5×Lags shifts in mix between paid and organic.Net revenue ÷ Number of ordersBrand-specificDiscount-driven AOV erodes margin faster than it lifts cash.Repeat purchase rate% buying again within 90 days30%+ at 90dSingle # hides cohort decay; report by acquisition month.T2Time to 2nd orderMedian days between order 1 and order 230–60 daysPower-user skew. Use median, not mean. Flagship Guide — Free Download ## The eCommerce Playbook Our master guide: 50 pages of everything we know about scaling online brands profitably — channel economics, ROAS, margin design, stock, cash and exit value. Your Name(Required)CompanyEmail(Required) Submit Join our eCommerce playbook list. 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Whether it’s for help with cash, margin, stock or messy numbers, please book in. [Talk to an Expert](https://ascendantaccountants.com/ecommerce-finance/discover-ecommerce-finance/) ## eCommerce accounting — common questions 5 questions · click to expand 01Is ROAS enough on its own?+× No. ROAS isolated by platform routinely double-counts conversions, ignores organic and email-driven revenue, and is sensitive to attribution model choice. Two campaigns with the same on-platform ROAS can have very different blended impact. Pair ROAS with MER (total revenue ÷ total marketing spend). MER is harder to game and surfaces the question that actually matters — is marketing in aggregate creating margin? 02How does AOV affect what we can spend on acquisition?+× Directly. If your trading margin per order is £18, you cannot spend £25 acquiring the customer and expect to survive on the first order. Lifting AOV widens the budget you can spend on Meta or Google without going under-water. The lever pairs with repeat. A modest AOV combined with a strong 90-day repeat rate gives you patience; a low AOV with a weak repeat rate forces ruthless CAC discipline. 03What is a healthy repeat-purchase rate?+× For consumables and apparel, 30%+ within 90 days is a good marker. For higher-consideration goods, the window stretches but the principle holds: customers who do not return inside 90–180 days rarely return at all. Always report by acquisition cohort. A single blended number can mask the fact that recent cohorts have collapsed while older ones prop up the average. 04How do we calculate trading margin properly?+× Start from net revenue (after returns and discount leakage). Deduct COGS at fully-loaded landed cost. Deduct fulfilment (3PL, packaging, last-mile carriage). Deduct variable marketing — every pound of Meta, Google, marketplace and influencer spend that scales with revenue. What is left is trading margin. Do not allocate overhead inside it. Overhead belongs in the next step — operating margin — because mixing the two destroys channel and SKU comparability. 05Why does time-to-second-order matter more than total repeat?+× Cash. A second order at 30 days repays acquisition while you are still spending into the next cohort. A second order at six months means you have funded six months of working capital with hope. It is also the most honest signal of product fit. People who genuinely love the product come back fast — long gaps suggest the first purchase was driven by discount or one-time intent.