CAC, LTV and ROAS explained for agency owners, with the formulas

CAC (Customer Acquisition Cost) is your total sales and marketing spend divided by the number of new customers acquired in a period; LTV (Lifetime Value) is the total revenue (or ideally profit) a customer generates over their entire relationship with you; and ROAS (Return on Ad Spend) is revenue from a specific campaign divided by what you spent on it. Used correctly, together, they tell you whether a client's marketing is actually profitable; used alone, each one can tell a misleadingly rosy story. This is the exact framework behind Omevia Intelligence's Marketing & Sales Analytics service.

CAC: the formula and the trap

CAC = total marketing and sales spend ÷ number of new customers acquired, over the same period. The most common mistake is calculating it per-channel using only that channel's ad spend, while ignoring the salary cost of whoever manages the campaigns, which quietly understates the true number and makes a channel look more efficient than it is. For agency reporting, a consistent, clearly agreed CAC formula across all clients matters more than a theoretically 'perfect' one that nobody applies the same way twice.

LTV: the number that actually matters most

LTV = average order value × purchase frequency × average customer lifespan (or, more precisely for subscription businesses, monthly revenue per customer ÷ monthly churn rate). LTV is arguably the most important of the three numbers here because it's the only one that captures whether a customer relationship is actually worth what it cost to create. A client with excellent CAC and poor LTV is often in worse shape than one with the reverse, even though the CAC number alone would look like the healthier story.

ROAS: useful, but easy to misread

ROAS = revenue generated ÷ amount spent on that campaign, commonly expressed as a multiple: a ROAS of 4x means £4 of revenue for every £1 spent. It's the metric most ad platforms surface by default, which is exactly why it gets over-relied on. ROAS measures revenue, not profit, so it says nothing about product cost, discounting, fulfilment cost, or the agency's own fee. A campaign can show a strong ROAS while contributing very little real profit once those are accounted for.

The ratio that ties them together

The most useful single number for judging whether a client relationship is healthy is the LTV to CAC ratio, commonly cited as healthy above roughly 3:1, meaning a customer is worth at least three times what it cost to acquire them. Below that, a business can still grow, but profitability stays thin, and any slowdown in acquisition quickly exposes the underlying problem that a good ROAS number had been quietly hiding.

A worked example

Take an illustrative client spending £10,000 a month on ads to acquire 100 new customers: CAC is £100. If those customers spend an average of £40 per order, twice a year, for an average of two years, LTV is £160. That's an LTV to CAC ratio of 1.6:1, growth technically, but thin margin for error, and a clear signal to either lift AOV and repeat purchase rate or bring CAC down before scaling ad spend further.

Reported on ROAS alone, that same client might look perfectly healthy: a strong-looking multiple on ad spend, with no visibility into the thin LTV to CAC ratio sitting underneath it. That gap between what ROAS shows and what the ratio actually reveals is exactly why agencies who report only ROAS tend to get blindsided when a client's growth suddenly stalls.

How often to recalculate these numbers

CAC is worth recalculating monthly, since ad costs and campaign performance shift quickly enough that a stale figure loses relevance within weeks. LTV is more stable and holds up fine recalculated quarterly, since customer lifespan and repeat behaviour move slowly by comparison. ROAS is usually reviewed at the campaign level, in real time, inside the ad platform itself. Mismatching these cadences, treating LTV as if it needs the same weekly attention as ROAS, is a common source of noisy, low-signal reporting that erodes a client's trust in the numbers over time.

Why agencies struggle to report this cleanly

Most agencies can report ROAS easily, because ad platforms calculate it natively inside the interface. CAC and LTV are harder, because they require connecting ad spend data to actual client revenue and retention data, often sitting in a completely separate CRM or e-commerce platform the agency doesn't have native access to. That connection work, not the formulas themselves, is usually the real blocker to reporting this properly every month.

Common reporting mistakes agencies make

• Reporting blended CAC across all channels, hiding which specific channels are actually profitable
• Using ROAS as a stand-in for profitability, without ever checking it against margin
• Calculating LTV once at the start of a client relationship and never revisiting it as behaviour changes
• Leaving out the agency's own management time when calculating true CAC

How we help agencies close that gap

We build dashboards that pull ad platform data alongside actual client sales or CRM data into one shared view, so CAC and LTV sit next to ROAS rather than living in a separate spreadsheet nobody updates. For agencies managing several clients at different growth stages, this often pairs well with our Forecasting & Predictive Analytics service, which flags early churn risk before it shows up in a client's monthly numbers.