Power BI Developer Interview Questions UK: 8 Real Questions and What Interviewers Want

Before your Power BI Developer interview, it helps to see the questions from the interviewer's side. We have picked eight from our set of 16 and added the reason each one gets asked.

Eight Power BI Developer interview questions, and what the interviewer is thinking

1. Explain the difference between Import, DirectQuery and Composite storage modes in Power BI, and how you decide which to use.

Why they ask: Storage mode choice drives performance, freshness and cost, so it is one of the most common Power BI interview questions.

2. What does CALCULATE do in DAX, and what is the difference between row context and filter context?

Why they ask: This tests genuine DAX understanding, which separates developers from report builders.

3. How would you design a data model in Power BI, and why do you prefer a star schema?

Why they ask: Model design determines performance and accuracy, and is central to the role.

4. A Power BI report takes too long to load. Which tools would you use to find the cause, and what would you try?

Why they ask: Performance tuning is a daily reality for Power BI developers.

5. What is query folding in Power Query, and how can you tell whether it is happening?

Why they ask: Folding affects refresh speed and source load, and indicates real hands-on Power Query experience.

6. Two senior stakeholders each ask for a different set of KPIs on the same executive dashboard. How would you handle it?

Why they ask: Developers must manage conflicting requirements without building the wrong thing.

7. Tell me about a time you rebuilt or optimised a Power BI solution that was performing badly or was difficult to maintain.

Why they ask: To judge real experience of improving legacy reports and the impact you delivered.

8. What do you enjoy about being a Power BI developer, and how do you keep your skills current as the platform changes so quickly?

Why they ask: To test genuine engagement and learning habits, given the monthly release cycle of the tool.

A sample answer to question 1

Explain the difference between Import, DirectQuery and Composite storage modes in Power BI, and how you decide which to use.

Import loads a compressed copy of the data into the VertiPaq engine, which gives the fastest visuals and full DAX and Power Query support, but data is only as fresh as the last refresh and is subject to dataset size limits. DirectQuery leaves data in the source and sends queries at report time, so it is always current and handles very large volumes, but performance depends on the source, and some DAX and transformations are restricted. Composite models mix both, for example importing small dimension tables while keeping a large fact table in DirectQuery, often with aggregation tables to speed up common queries. My default is Import with scheduled or incremental refresh, because it gives the best user experience. I would choose DirectQuery only where near real-time data is genuinely needed or data cannot leave the source, and I would then optimise the source with indexes and views. With Fabric, Direct Lake is also worth considering.

Common mistake to avoid: Saying DirectQuery is always better because it is live; ignoring source performance

Want the rest?

Full model answers, key points and common mistakes for all 16 questions are on the Power BI Developer interview questions page. The first five are free, no sign-up needed.