CAC and LTV explained. The ratio that tells you if your growth is working.

The short answer.

CAC stands for Customer Acquisition Cost. LTV stands for Lifetime Value (sometimes written CLV or CLTV). The CAC LTV ratio puts those two numbers together to tell you whether your business model is actually working.

If your LTV is £9,000 and your CAC is £3,000, your LTV:CAC ratio is 3:1. That is the number most investors and operators treat as the floor for a healthy SaaS business, based on benchmarks published by David Skok in his widely cited "SaaS Metrics 2.0" analysis (For Entrepreneurs blog, 2010) and referenced by Bessemer Venture Partners across their State of the Cloud reports.

Below 1:1 means the business is structurally unprofitable at the unit level. Between 1:1 and 2:1, margins are thin and the model is fragile. At 3:1, the unit economics hold and the business can invest in growth. Above 5:1, the ratio often signals that you are being too cautious with acquisition spend and leaving revenue behind.

Why it matters.

Revenue figures alone do not tell you much. A company growing at 40% per year can still be destroying value if it costs more to acquire each customer than that customer ever pays back. The CAC LTV ratio is the check on that.

It matters in three specific situations.

• Fundraising. Investors will ask for it. If you cannot produce it cleanly, that is a signal about your data infrastructure, not just your numbers.
• Channel decisions. When you are comparing paid search against outbound sales or partner referrals, CAC by channel tells you where to put the next pound. LTV by segment tells you which customers are worth paying more to win.
• Churn management. LTV is directly linked to churn rate. If churn rises, LTV falls, and a ratio that looked healthy six months ago may now look marginal. Tracking this over time catches problems before they compound.

The ratio also connects teams that typically work in silos. Marketing owns CAC. Customer success owns retention, which drives LTV. Finance sees both in the P&L but often months after the fact. A proper revenue operations setup puts the ratio in front of all three teams on the same cadence, so decisions about spend and retention are made with the same data.

How it is measured or applied.

Both calculations are straightforward once you agree on the inputs.

Calculating CAC

Take your total sales and marketing spend in a given period (salaries, tools, ad spend, agency fees, events) and divide by the number of new customers acquired in that same period.

CAC = total sales and marketing spend / new customers acquired

The most common mistake is mismatching the period. If you spent heavily in Q4 on campaigns that converted in Q1, a straight quarterly calculation will overstate Q4 CAC and understate Q1 CAC. Some teams use a 90-day lag to account for sales cycle length. Choose a convention and keep it.

Calculating LTV

For subscription businesses, the most reliable formula is:

LTV = (average monthly revenue per customer x gross margin) / monthly churn rate

If you do not yet have reliable churn data, a simpler version works as a starting point:

LTV = average monthly revenue per customer x average customer lifetime in months

Gross margin matters here. If you are running at 60% gross margin, a customer paying £1,000 per month contributes £600 per month in gross profit. That is what you are comparing against CAC, not the top-line revenue figure.

The payback period check

One number the LTV:CAC ratio does not capture on its own is timing. A 3:1 ratio sounds healthy, but if it takes four years to realise that value, you have a cash flow problem in the meantime.

That is where CAC payback period comes in:

Payback period = CAC / monthly gross profit per customer

Bessemer Venture Partners benchmarks 12 to 18 months as the healthy range for B2B SaaS. Beyond 18 months, capital efficiency becomes a genuine concern. You are effectively lending money to your customers for a year and a half before you break even on acquiring them.

A practical example.

Say you run a B2B SaaS product. Your numbers for the last quarter look like this:

• Total sales and marketing spend: £90,000
• New customers acquired: 30
• Average monthly revenue per customer: £800
• Gross margin: 70%
• Monthly churn rate: 2%

CAC = £90,000 / 30 = £3,000

LTV = (£800 x 0.70) / 0.02 = £560 / 0.02 = £28,000

LTV:CAC ratio = £28,000 / £3,000 = 9.3:1

At first glance, that looks excellent. But check the payback period.

Monthly gross profit per customer = £800 x 0.70 = £560

Payback period = £3,000 / £560 = 5.4 months

A ratio of 9:1 with a payback period of just over five months is a strong signal that you could be spending more on acquisition. You are recovering your CAC in well under a year and leaving significant headroom to grow. The conversation then shifts to where to invest: more paid channels, a larger sales team, a partner programme.

If the same business had a monthly churn rate of 8% instead of 2%, LTV would drop to £7,000, the ratio would fall to 2.3:1, and the payback period would still be 5.4 months. The payback looks fine, but the model is fragile. In that scenario, the priority is retention, not acquisition spend.

This kind of analysis is the day-to-day work of a RevOps function. If you want someone to help you build the metrics infrastructure and translate the numbers into a growth plan, RevOps consulting is where that work starts.