- CAC is everything spent winning customers divided by the customers won. Include your own selling time.
- Calculate lifetime value in gross profit, never revenue. Using revenue flatters the result by the size of your cost of sale.
- An LTV to CAC ratio of 3:1 or better is the usual benchmark. Below 1:1 you lose money on every customer.
- Payback period decides how fast you can grow. Under 12 months and growth largely funds itself.
Three numbers tell you whether marketing is an investment or a leak. I will shout about your business all day, but only once these say it is worth it.
Most small business marketing decisions are made on impressions. A campaign felt busy, the phone seemed to ring, so it probably worked. That is a reasonable instinct and a poor basis for deciding where the next few thousand pounds goes.
Three numbers turn it into something you can actually reason about. This guide explains each one and how they fit together. The CAC and payback calculator will do the arithmetic on your own figures.
What a customer costs you to win
Customer acquisition cost is the simplest of the three. Add up everything spent on winning new customers in a period, and divide by the number of new customers won.
Spend £2,000 a month and win 10 customers, and your CAC is £200.
Include: advertising, agency and freelancer fees, content production, marketing software, event costs, and the salaries or commission of anyone doing marketing or selling. If you do the selling yourself, put a realistic cost on your time. Leaving it out is the most common way small businesses arrive at a CAC that looks far better than it is.
Exclude: the cost of delivering to customers you already have, and general overheads like rent. Those belong in gross margin and fixed costs.
What a customer is worth
Lifetime value is what a customer contributes across the whole relationship. The critical detail is that it must be measured in gross profit, not revenue.
A £500 order at a 60% gross margin contributes £300, not £500. Using revenue makes every ratio look roughly twice as healthy as it is, and it is the single most common error in this calculation.
At £300 gross profit per order, two orders a year, retained three years, lifetime value is £1,800.
Do not agonise over precision. If you have been trading long enough to know roughly how often customers buy and roughly how long they stay, that is enough to make decisions with. If you are too new to know, use conservative estimates and revisit in six months.
Putting them together
Neither number means much alone. A £500 CAC is excellent if customers are worth £5,000 and ruinous if they are worth £400. The ratio is what tells you which.
| LTV to CAC | What it means | What to do |
|---|---|---|
| Below 1:1 | You lose money on every customer you win | Stop spending. Fix conversion, margin or retention first. |
| 1:1 to 3:1 | Profitable but thin, with little room for a bad month | Improve before scaling. Small conversion gains move this a lot. |
| 3:1 to 5:1 | Healthy. The usual target. | Scale carefully, watching whether CAC rises as you spend more. |
| Above 5:1 | Often means you are underinvesting | Spend more. You are leaving growth on the table. |
It usually means you are not spending enough to find the customers who are out there. If acquisition is comfortably profitable and you have capacity to deliver, the right move is to increase spend until the ratio comes down towards 3:1.
Why payback decides how fast you can grow
Ratios do not pay wages. A business can have an excellent 5:1 ratio and still run out of cash, because the value arrives over four years while the acquisition cost is paid today.
Payback measures how many months of a customer's gross profit it takes to recover what they cost to acquire. Under twelve months, growth largely funds itself. Much beyond that and scaling requires external cash.
Move the sliders to see how the three numbers interact.
Where to improve first
When the economics are not working, the instinct is to cut marketing spend. That lowers CAC and lowers customers won by roughly the same proportion, so the ratio barely moves. These four levers move it properly, roughly in order of how quickly they pay off.
- Conversion rate. Usually the cheapest win. Going from 20% to 25% of leads converting cuts CAC by a fifth with no extra spend. Faster response times, clearer proposals and fewer steps in the enquiry process all move this.
- Retention. Keeping customers an extra year raises lifetime value directly and costs a fraction of winning a new one. It is also the most neglected of the four in small businesses.
- Purchase frequency. Getting existing customers to buy more often is far cheaper than finding new ones. Service reminders, maintenance plans and simple follow-ups do most of the work.
- Price and margin. A price rise flows straight into gross profit per order, raising lifetime value without touching acquisition at all. See the pricing guide.
Acquisition cost is rarely flat. The first customers from any channel are usually the cheapest, because you start with the most interested audience. As you spend more you reach people who are harder to convince, and CAC rises. Recheck the ratio at each new level of spend rather than assuming it holds.
Tracking this without a big system
You do not need attribution software. You need to ask every new customer how they found you, and write the answer down somewhere consistent.
A minimum viable tracking setup
0 of 7Self-reported attribution is imperfect. People forget, or name the last thing they saw rather than the thing that convinced them. It is still far better than nothing, and the trend over several quarters is reliable even when individual months are not.
