# CAC, ROAS and payback

How ProductLense computes customer acquisition cost, return on ad spend and payback per channel, and when each is left empty.

The three ratios on the Profit page use the same key (channel, source, medium and campaign) and period as [profit per channel](/docs/profit/profit-per-channel). They appear only where there is ad spend.

## Customer acquisition cost

```text
CAC = Ad spend ÷ customers, for the same channel and range
```

Customers are distinct customers with a first succeeded charge in the range (new customers). CAC is null when customers = 0.

## Return on ad spend

```text
ROAS = Revenue ÷ Ad spend
```

Revenue is charges − refunds − chargebacks, before processor fees. ROAS is null when spend = 0. A ROAS above 1.0 does not by itself mean profit: profit also subtracts fees (Profit = Revenue − Fees − Ad spend).

## Payback

```text
Payback = CAC ÷ average first-month net revenue per new customer
```

Net revenue is Revenue − Fees. Payback is the number of months it takes a new customer to earn back what it cost to acquire them, assuming they keep paying the same. It is empty when CAC is null or first-month net revenue is 0.

## Example

```text
revenue                       2,407.00
fees                            152.00
ad spend                      1,518.00
new customers                       31
CAC            1,518.00 ÷ 31 =   48.97
ROAS        2,407.00 ÷ 1,518.00 =  1.59
first-month net revenue         899.00
per new customer  899.00 ÷ 31 =  29.00
payback          48.97 ÷ 29.00 =  1.69 months
profit  2,407 − 152 − 1,518 =   737.00
```

Figures are rounded to cents, and ratios to two decimals.

## Related

- [Add ad spend](/docs/profit/ad-spend)
- [How payments are attributed](/docs/revenue/attribution)