Return on investment (ROI) is the most fundamental marketing metric: it measures the net profit generated by a marketing activity as a percentage of its cost. A positive ROI means the activity generates more value than it costs; a negative ROI means it destroys value. In practice, calculating marketing ROI requires correctly attributing revenue to specific activities — which is straightforward for direct-response channels like paid search and email, but harder for brand campaigns, SEO, and content marketing where impact is indirect or takes time to materialise. Despite the attribution challenges, attempting to measure ROI — even imperfectly — produces better marketing decisions than not measuring it at all.
ROAS (Return on Ad Spend) is a top-line advertising efficiency metric used primarily within paid media. It measures gross revenue generated per pound of ad spend, without accounting for the cost of goods or other expenses. ROAS is most useful for day-to-day optimisation decisions within ad platforms — identifying which campaigns, ad groups, or audiences are generating revenue most efficiently. However, a high ROAS does not guarantee profitability: a campaign generating £5 in revenue for every £1 in ad spend (5x ROAS) is profitable only if gross margins are above 20%. Always cross-reference ROAS against gross margin to determine the minimum ROAS required for a campaign to break even.
Customer Acquisition Cost (CAC) and Customer Lifetime Value (LTV) are the two metrics that most directly determine whether a business model is financially viable at scale. CAC is the total sales and marketing spend divided by the number of new customers acquired in a period. LTV is the total net revenue expected from a customer over their entire relationship with the business — typically calculated as average order value multiplied by purchase frequency multiplied by customer lifespan, minus the cost to serve. The LTV:CAC ratio is the single most important metric for assessing marketing efficiency: a ratio below 1:1 means acquisition costs exceed customer value, which is unsustainable; 3:1 or above is the benchmark for a healthy, scalable business.
Churn rate — the percentage of customers lost in a given period — is the invisible drain on business growth. Because churn compounds over time, even a seemingly small monthly churn rate of 3–5% results in losing a third to half of the customer base each year. The revenue impact is often underestimated: losing a customer who would have generated £1,000 of gross profit over two years is not a single lost sale — it is the loss of the entire future revenue stream from that relationship. Reducing churn by even 1 percentage point typically has a larger impact on long-term revenue than equivalent increases in new customer acquisition, because every retained customer continues to contribute without additional acquisition cost.
Conversion rate optimisation (CRO) is one of the highest-return marketing activities available to businesses with existing traffic. The conversion rate measures the percentage of visitors who take a desired action — making a purchase, completing a form, or signing up for a trial. Improving conversion rate from 2% to 2.5% on a landing page receiving 10,000 visitors per month increases conversions from 200 to 250 — a 25% increase in output from the same traffic. At a CAC of £50 per conversion, that is £2,500 of additional customer value without spending an extra pound on acquisition. The Conversion Rate Calculator models the revenue impact of any improvement in conversion rate so you can prioritise CRO investment relative to acquisition spend.
Budget allocation is the strategic decision of how to distribute marketing spend across channels to maximise total return. Effective allocation requires channel-level data: the CAC, LTV, and ROAS for each acquisition source. Channels with the lowest CAC and highest LTV should receive the most budget; channels with a negative ROI should be reduced or eliminated. A common framework allocates 70% of budget to proven high-return channels, 20% to growing or emerging channels, and 10% to experimental activity. The Marketing Budget Allocation Calculator on this page models expected revenue, profit, and blended ROI across up to eight channels simultaneously.