Take the ACV, compound it with net churn to it to obtain LTV.

Add the cost of your sales and marketing and divide by the number of deals during that time to obtain CAC.

Then you can calculate both LTV/CAC and CAC payback.

Doesn’t that have to assume that all deals came through advertising? In my case I find more and more sales are word of mouth or from organic search, but it’s very hard to measure (at least in B2B).

CAC is an aggregate measure, for all sales and marketing costs.

Per channel attribution is of course far more difficult, depending on the channel.