Allowable CAC Calculator
Most teams measure CAC after the fact. Allowable CAC flips it: it is the ceiling you set before you spend. Enter what a customer is worth and the return you require — the tool gives you the most you can afford to pay to win one and still hit your target.
Allowable CAC = gross-profit lifetime value ÷ target LTV:CAC ratio. It is the maximum you can pay to acquire a customer and still earn your required return. Build the lifetime value from average revenue per account, gross margin and expected lifespan — ARPA × gross margin × lifespan — then divide by the ratio you want (commonly 3:1). The result is a hard spending ceiling: hold every channel and campaign to it, and growth stays profitable by construction rather than by hope.
Allowable CAC Calculator inputs and result
How to use this calculator
- Build the customer's valueEnter average revenue per account per period, your gross margin, and how many periods a customer stays. The tool multiplies them into gross-profit lifetime value — the real worth of a customer, not their revenue.
- Set your target LTV:CAC ratioChoose the return you require. 3:1 is the widely used healthy target; a stricter ratio sets a lower, more conservative allowable CAC.
- Read your allowable CACThe tool divides gross-profit LTV by the ratio to give the maximum you can afford to pay per customer. This is the ceiling, not a goal — efficient channels should come in well under it.
- Compare your actual CACEnter your current CAC to see headroom or overspend. Under the ceiling means room to scale; over it means lift LTV or cut CAC before adding budget.
- Export your numbersCopy a share link, download the CSV for your planning model, or print a one-page PDF for the budget-setting conversation.
RGM Expert Says
Allowable CAC is the discipline that turns unit economics from a scorecard into a budget. Most teams compute CAC after the quarter and react; the operators who compound decide the ceiling first and hold every channel to it. We set allowable CAC at the start of a plan so that the question stops being ‘was that efficient?’ and becomes ‘is this bid under the line?’ — a question a media buyer can answer in real time.
The input that quietly does the work is gross margin. Allowable CAC must be built on gross-profit lifetime value, never revenue, because a high-revenue customer on a thin margin is worth far less to acquire than they appear. We have watched teams set generous CAC ceilings off revenue LTV and slowly bleed, because the margin was never in the math. Run the value through margin first and the ceiling tells the truth.
We treat allowable CAC and marginal CAC as a pair. Allowable CAC sets the line you must not cross; marginal CAC tells you where each channel actually sits as you scale. The job is to push spend until marginal CAC approaches allowable CAC, then stop — that is the profitable frontier, and having both numbers makes it a calculation rather than a guess.
How it works
Allowable CAC reasons backward: from what a customer is worth and the return you demand, to the most you can pay to win one.
- ARPA — average revenue per account, per period.
- Gross margin — share of revenue left after the cost to serve; converts revenue into profit value.
- Expected lifespan — periods a customer stays; the inverse of churn rate.
- Target LTV:CAC ratio — the return you require per acquisition dollar; divides LTV into the allowable ceiling.
Gross-profit LTV here uses the simple ARPA × margin × lifespan form; it does not discount future cash flows. For long lifespans, a discounted LTV is more conservative. The 3:1 target ratio is popularised in David Skok’s SaaS Metrics 2.0.
Why set the ceiling before you spend
Reactive CAC management is always a step behind: by the time the quarter’s CAC is in, the money is spent. Allowable CAC moves the decision forward. Derive the most you can pay per customer from lifetime value and a target return, and you have a line every bid, channel and campaign can be judged against in the moment — profitability designed in, not discovered later.
The number lives or dies on gross margin. Allowable CAC must be built on gross-profit lifetime value, because acquisition is paid out of profit, not revenue. A customer worth $2,400 in revenue but only $600 in gross profit cannot support a $700 CAC, however tempting the revenue figure looks. Run value through margin first, and the ceiling reflects what the business can actually afford.
Allowable CAC pairs naturally with marginal CAC. Allowable CAC sets the limit; marginal CAC shows where each channel sits as you scale. Push spend until marginal CAC nears allowable CAC, then hold — that intersection is the profitable frontier. Together the two turn ‘how much should we spend?’ from a debate into arithmetic.
How the target ratio sets your ceiling
Allowable CAC scales inversely with the target ratio you choose: a stricter ratio buys more safety at the cost of a lower ceiling. These illustrate the trade-off on a fixed gross-profit LTV; the 3:1 target is the common rule of thumb.
| Target LTV:CAC | Stance | Allowable CAC (on $1,800 LTV) |
|---|---|---|
| 2 : 1 | Aggressive — thin safety margin | $900 |
| 3 : 1 | Balanced — the common healthy target | $600 |
| 4 : 1 | Conservative — more cushion | $450 |
| 5 : 1 | Cautious — likely underinvesting | $360 |
What operators say about CAC discipline
Decide what a customer is worth and what return you need, and the maximum you can pay to acquire one falls out of the math; spending past that line is a choice to lose money.
Set the acquisition ceiling from lifetime value first; the teams that compound run spend against a known limit rather than discovering it after the fact.