A plain-English guide to the five marketing metrics that actually matter: CAC, LTV, ROAS, MER, and payback period, and how to calculate each from data you already have.
You don't need a marketing degree to understand whether your marketing is working. You need five numbers, defined clearly, and a sense of what good actually looks like for a business your size. This is the guide we'd want if we were on the other side of the table, reading a report from someone else and needing to ask a smart question instead of quietly nodding along.
Customer acquisition cost, usually shortened to CAC, is the total cost to acquire one new customer, including ad spend and often the people or tools involved in running acquisition. To calculate it, divide total marketing spend for a period by the number of new customers gained in that same period. If you spent $10,000 last month and gained 50 new customers, your CAC is $200.
There's no universal good number here, and anyone who tells you there is hasn't asked the right follow-up question. A $200 CAC is excellent for a business where a customer is worth $2,000 over their lifetime, and it's unsustainable for a business where that same customer spends $150 once and never returns. CAC only means something in relation to the next metric.
Customer lifetime value, or LTV, is the total revenue a typical customer generates over the full length of their relationship with your business, not just their first purchase. A simple version to calculate: average order value multiplied by average number of purchases per year, multiplied by average number of years a customer stays. If your average order is $80, customers buy three times a year, and stay for two years on average, your LTV is $480.
The relationship between LTV and CAC, often expressed as a ratio, is one of the clearest single signals of business health available. A ratio of 3 to 1 or higher is generally considered healthy. Below 1 to 1 means you are losing money on every customer you acquire, even if the top-line revenue number looks fine on a monthly dashboard.
Return on ad spend, or ROAS, is total revenue generated from advertising divided by the total amount spent on that advertising. Blended ROAS specifically means calculating this across every channel combined, not the platform-reported number from a single channel viewed in isolation. Divide total revenue attributed to paid ads by total ad spend across all channels for the same period. $40,000 in revenue from $10,000 in total ad spend is a 4x blended ROAS.
The number that actually determines whether that 4x is good or bad is your break-even ROAS, calculated as 1 divided by your gross margin percentage. A business with 30 percent gross margins needs at least a 3.3x ROAS just to break even on ad spend, meaning anything below that is losing money on every ad dollar spent, even while revenue is visibly climbing and it feels like the ads are working.
Marketing efficiency ratio, or MER, is total revenue divided by total marketing spend across every channel, including things that aren't ad platforms at all: content production, email tools, organic social management, agency fees. This is the widest-lens efficiency number available to a business, and it catches problems that channel-specific metrics miss entirely.
MER is useful precisely because ROAS can look strong on a single ad channel while the overall marketing program is inefficient due to high overhead sitting elsewhere in the budget. If your ROAS looks healthy but your MER is weak, the problem usually isn't the ads themselves. It's everything else in the marketing budget that isn't being measured with the same scrutiny.
Payback period is how long it takes to earn back what you spent to acquire a customer, in actual revenue collected from that customer over time. A business can have excellent LTV to CAC economics on paper and still run into serious cash flow trouble if the payback period is too long relative to how fast the business needs to reinvest that cash into the next round of acquisition. A 12-month payback period requires a fundamentally different cash management approach than a 30-day one, even when the lifetime economics are identical on a spreadsheet.
If you only have time to ask one question about your marketing data on your next call, ask this: what's our break-even ROAS, and are we currently above or below it? It's a specific, answerable question that forces a real number rather than a vague reassurance, and if the person on the other end can't answer it quickly and confidently, that tells you something worth paying attention to as well.
Start with whatever window of clean data you do have, even just the last 60 to 90 days, rather than waiting for a full year of perfect records. These metrics are more useful as an ongoing habit you build going forward than as a single perfect historical calculation. Approximate numbers calculated consistently beat perfect numbers calculated once.
Your ad platform, whether Google or Meta, only reports on conversions it believes it influenced within its own attribution window, and both platforms tend to be generous in crediting themselves. Blended ROAS pulls in your actual total revenue and total spend across every channel combined, which is almost always a more conservative and more accurate number than any single platform's self-reported figure.
CAC and payback period matter most in the earliest stages, because cash constraints are usually the binding limitation before lifetime value has had time to prove out. LTV becomes more reliable to calculate once you have at least a year of repeat customer behavior to draw from, and MER becomes more useful once you're running marketing spend across more than one or two channels.
Read the fuller breakdown of what actually counts as a performance marketing metric versus a vanity number, and the exact ROAS formula we use in every engagement. If reading your own numbers still feels like translating a foreign language on every call, a Growth Gap Analysis is built to walk through exactly this, in plain English, using your actual numbers.
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