Cost per enquiry is a simple division: assigned costs divided by the number of enquiries. The arithmetic is easy. Defining which costs and which enquiries belong in the calculation is harder. Without a consistent definition, two reports can show different figures for the same campaign while both remain mathematically correct.
Name the cost base
If the calculation includes advertising spend alone, label it “advertising cost per enquiry”. If design, management or other directly assigned work is included, say so in the report. Do not compare a figure containing agency fees with another containing only platform charges.
In an invented example, a campaign incurs €360 in advertising spend and generates eighteen genuine enquiries. Advertising cost per enquiry is €20. Add €180 in assigned design work and the total becomes €30 per enquiry over the same period. Neither figure is inherently wrong; each answers a different question.
One-off setup work can have a large effect in the first month. Show it separately rather than silently spreading it across an arbitrary number of months. A longer-term view can also use the total costs and enquiries over a stated period, provided its boundaries remain clear.
Clean the enquiry count
Do not count test submissions, spam or accidental duplicates as new business enquiries. If someone submits a form and then telephones, that may be one project with two contacts. Establish a straightforward counting rule and apply it consistently in every reporting period.
Separate genuine enquiries from suitable enquiries. With €360 of spending, eighteen genuine enquiries and twelve suitable enquiries, the respective figures are €20 and €30. Neither establishes that twelve sales occurred. Orders won remain a separate outcome.
Maintain a brief note explaining any adjustment to the count. It is much easier to understand “two duplicate messages removed” than to reconstruct an unexplained change several months later. Avoid collecting extra personal details solely to make the marketing calculation more elaborate.
Compare periods on the same basis
A click near the end of a month may produce an enquiry during the following month. For small volumes, avoid drawing conclusions from individual days alone. Record whether the report uses the date an enquiry arrived or a platform attribution method. Those approaches can produce different totals and should not be placed side by side without explanation.
When there are no enquiries, the division is undefined. Report “no enquiries during this period” and show the spending. A value of €0 would be misleading because it suggests that enquiries were acquired at no cost.
A lower cost per enquiry is not automatically a better business outcome. Check whether the service mix, suitability, handling effort or eventual order value changed. An inexpensive contact about a service the company does not provide has little value to that company. Read the metric alongside suitable enquiries and actual orders, keeping each stage distinct. The purpose is to understand what the spending produced, not to manufacture the smallest possible number.
