Cost per lead is the number vendors compete on, which is a good reason to be suspicious of it. It is easy to lower and it says nothing about whether the money produced anything.
The arithmetic
Cost per retained case is total acquisition spend for a period divided by the number of signed cases attributable to that spend. That is the whole calculation. The difficulty is not the maths, it is being honest about the inputs.
Total spend means everything: media, vendor fees, and a fair allocation of the intake labour spent working those records. Firms that exclude intake cost are measuring the vendor rather than the channel.
Why cheap leads get expensive
Suppose one source is half the price of another. If its records take twice as many intake attempts to reach, and a third as many convert, the cheap source is substantially more expensive per signed case — and it consumed intake capacity that could have gone somewhere better. That second cost never appears on an invoice.
This is why cost per lead comparisons between sources are close to meaningless without conversion data attached. The only fair comparison is at the far end of the funnel.
Attribution windows
Workers’ compensation matters do not sign the same day. If you divide this month’s spend by this month’s signings, you are comparing two different cohorts and the number will swing wildly for reasons that have nothing to do with performance.
Track by cohort instead: take the records that arrived in a given month and follow them until they resolve. It is slower, it means waiting before you can judge a new source, and it is the only version of the number that means anything.
Sample size discipline
A handful of records is not a verdict on a source. Case type mix, seasonality, and which intake specialist happened to work the queue all move small samples around. Firms regularly cancel campaigns on evidence that would not survive a moment’s scrutiny, and re-start them on evidence just as thin.
What the number is for
Cost per retained case sets a ceiling. Against your average case value and your capacity to take work, there is a figure above which acquisition stops making sense. That figure is the constraint every other marketing decision should be tested against.
It also changes the conversation with vendors. A firm that knows its cost per retained case can talk about whether a source is worth its price rather than haggling over a per-lead rate that predicts nothing.