I have a brief answer to this question. In my experience about 75% of the clients I work with have between 5 and 15 sessions, on average. This can be regarded as short to medium term therapy.

About 25% of the people I work with will have upwards of 20 sessions, sometimes working for over a year or more, which can be regarded as long-term therapy.

In addition to regular feedback in each session, periodic reviews take place every 5-6 sessions to assess progress. This allows the course of therapy to be checked and discussed openly so that both the client and counsellor know where the therapy is going and what the goals are in the process.