A client case study is a testimonial with the working shown, and the reason most businesses publish two a year is not the writing. It is the approval. This page is the route from a quote you already hold to a published study, with the arithmetic: on the worked example 18 testimonials a year yield 7 interviews, 5 published studies, 43 hours and $2,376 of somebody's time, which is $440 for each one that reaches the site.
Start from a testimonial, never from a blank page
The candidates are the quotes that already carry a number. Going back to a client who has told you something specific is a twenty-minute call; approaching a client cold for a case study is a project. It also means the client has already agreed to be quoted once, which is the hardest yes in the sequence.
Interview for the two numbers
What it was before and what it is now. Everything else in the study exists to make those two credible, and a study with no number in it is a long testimonial. If neither number exists, the interview is telling you something useful: this client is a quote on a services page rather than a case study, and that is where the effort should go.
Budget for the approval, not the draft
On the worked example the customer takes about 2 weeks to approve and a quarter of the drafts never survive it: 2 of 7 written and never published. Write for that, and never promise a launch date that depends on somebody else's legal team.
Questions people ask about client case study
How many case studies do we need?
Fewer than you think, in more places than you think. Five well-placed studies outperform twenty in an archive.
What if the client will not be named?
Anonymise by industry and size and keep the numbers. It is weaker, and it is still evidence.
Who should write it?
Whoever did the work, edited by whoever writes well. On the worked example six hours each including the interview, at $55 an hour.