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Preparing for a Power BI interview in 2026? This comprehensive guide covers the most frequently asked questions across freshers and experienced levels, with detailed answers written by industry professionals. Each answer explains both the concept and how to articulate it clearly during an interview.
Roles these questions apply to: Power BI Developer, BI Analyst, Data Analyst, Report Developer
Expected salary range: ₹5–16 LPA
Core skills tested: Power BI Desktop, DAX, Power Query, Data Modelling
How to Use This Guide
- Read each answer carefully — understand the concept, don’t just memorize
- Practice explaining each answer aloud in your own words
- For technical questions, try implementing the concept hands-on
- Focus on questions relevant to your target role and experience level
- Prepare 2–3 real examples from your projects for each concept
Power BI Interview Questions with Answers
1. What is DAX and how is it different from Excel formulas?
DAX (Data Analysis Expressions) is Power BI’s formula language for creating calculated columns, measures, and tables. Unlike Excel (cell-based), DAX operates on entire columns and tables using filter context. Key difference: DAX measures evaluate dynamically based on the visual’s context (which filters/slicers are active), while calculated columns compute once at refresh time. DAX is more powerful but requires understanding row context vs filter context.
2. Explain the difference between Calculated Columns and Measures.
Calculated Columns: computed at data refresh, stored in the model, consume memory, evaluated row-by-row (row context), can be used in slicers/filters. Measures: computed at query time, not stored, dynamic (recalculate based on filter context), cannot be used in slicers. Use columns for static categorisation; use measures for aggregations (SUM, AVERAGE, COUNT) that should respond to user interactions.
3. What is filter context in DAX?
Filter context is the set of active filters applied to a DAX calculation at evaluation time. Sources: slicers, visual filters, page filters, report filters, cross-filtering from other visuals, and relationships. CALCULATE() is the most important DAX function because it modifies filter context — adding, removing, or overriding filters. Understanding filter context is the key to mastering DAX.
4. How do you build a Star Schema data model?
Star Schema: central Fact table (transactions — sales, orders, events) surrounded by Dimension tables (descriptive — date, product, customer, geography). Relationships: one-to-many from dimension to fact. Benefits: optimal DAX performance, clear business semantics, reduced ambiguity. Avoid: many-to-many relationships, bidirectional filtering (unless necessary), and snowflake chains. The Date dimension is mandatory for time intelligence.
5. What is Power Query and when do you use it?
Power Query (M language) is the ETL tool within Power BI for data transformation. Use it to: connect to data sources, merge/append tables, pivot/unpivot columns, change data types, handle nulls, create custom columns, filter rows, and build reusable transformation steps. All steps are recorded and re-applied on each refresh. Do heavy transformations here rather than in DAX for better performance.
6. Explain Row-Level Security (RLS) in Power BI.
RLS restricts data access at the row level per user. Setup: create Roles in Power BI Desktop with DAX filter expressions (e.g., [Region] = USERNAME()), then assign users to roles in Power BI Service. Dynamic RLS uses a security table mapping users to allowed values — more maintainable than multiple static roles. Test with ‘View As Role’ before publishing.
7. What are Time Intelligence functions in DAX?
Time Intelligence functions calculate over time periods: TOTALYTD (year-to-date total), SAMEPERIODLASTYEAR (same period prior year), DATEADD (shift dates), PARALLELPERIOD (full periods offset), DATESYTD/DATESQTD/DATESMTD (date ranges). Prerequisite: a proper Date table marked as Date Table with continuous dates. These enable YoY comparisons, running totals, and period-over-period analysis.
8. How do you optimise Power BI report performance?
Optimisation strategies: reduce model size (remove unused columns, summarise where possible), use Star Schema, avoid bidirectional relationships, use variables in DAX (calculate once, use multiple times), prefer measures over calculated columns for aggregations, limit visuals per page (<15), use aggregations for large datasets, and check Performance Analyser to identify slow visuals/queries.
9. What is the difference between Import, DirectQuery, and Composite modes?
Import: data copied into Power BI model — fastest performance, scheduled refresh, size limits (1GB free, 10GB Pro). DirectQuery: queries sent to source database live — always current, no size limit, slower performance, limited DAX. Composite: mix both — import dimensions for speed, DirectQuery large fact tables. Choose based on data freshness needs vs performance requirements.
10. How do you implement incremental refresh?
Incremental Refresh loads only new/changed data instead of full reload. Setup: create RangeStart and RangeEnd parameters (DateTime type), filter source query using these parameters, define refresh policy (e.g., keep 3 years, refresh last 10 days). Power BI creates partitions automatically. Benefits: faster refresh, reduced source load, supports large datasets. Available in Pro/Premium.
Interview Preparation Tips for Power BI Roles
For Freshers
- Focus on core concepts and fundamentals (questions 1–5)
- Build at least 2 hands-on projects you can discuss in detail
- Prepare to explain your learning journey and motivation
- Practice coding/configuration challenges related to Power BI Desktop, DAX, Power Query, Data Modelling
For Experienced Professionals
- Prepare architecture and design discussions (questions 6–10)
- Have production war stories ready — problems you solved and lessons learned
- Be ready to whiteboard solutions and discuss trade-offs
- Show leadership through mentoring examples and process improvements
Prepare with Structured Training
Power BI Training at SkilBrill includes dedicated interview preparation with mock interviews conducted by hiring professionals. The programme covers all concepts tested in these questions through hands-on labs and real-world projects. Placement support with 200+ hiring partners. Call +91 8610964691.
