How many customer interviews should you plan?

Plan a small first round that you can review before arranging more. GOV.UK’s service research guidance suggests usually 4–8 participants per round for methods including in-depth interviews. Use that as a planning reference for one focused question and audience, not a total that proves demand for your product.

Count the interviews you actually have separately from invitations sent and calls booked. Sending eight invitations does not give you eight conversations. Leave room in your budget and calendar to adjust after the first round.

Review what you already know

Read your notes before paying for another interview. What can you now explain? Which unanswered question could change what you do next? The interview analysis guide shows how to check a conclusion against the original notes.

Repeated answers can be useful, but check whose answers they are. Several people doing the same job may describe a process well while leaving the buyer’s part unexplained. Equally, you may already have the detail you need and simply need to compare the notes.

You do not need another interview just to reach a round number. A useful stopping point is when you can make the decision you set out to make, or the remaining question needs a different kind of test.

Let the remaining question choose the next step

Suppose you have interviewed dispatchers at repair companies. Several describe waiting for the owner’s approval before changing a technician’s assignment. What to do next depends on what you still need to learn:

• Why was approval needed? Check whether your existing notes explain it. If they do not, a conversation with an owner who recently made that decision could help. Ask about that actual reassignment.
• Can a dispatcher use your proposed reassignment screen? Give them a realistic task and watch them try it. Another description of the old process will not show whether the new screen works.
• Will a company commit time or money to the tool? Make a concrete offer, such as a pilot with a defined price and workload, and see whether the company commits. Agreement that the current process is frustrating does not establish that.

The familiar “five users” recommendation concerns finding usability problems, improving a design and testing again. It is not a rule that five customer interviews establish demand.

Before arranging another paid call, name the question it should answer. Then choose someone with the relevant experience. In Instant Expert, review the displayed request price and explain that question in the invitation. The person decides whether to accept; plan your interview budget around that uncertainty.