Power BI
Why Your Power BI Report Is Slow and How to Fix It
A practical guide to finding and fixing the most common causes of slow Power BI reports.
A report opens slowly, slicers lag, and users stop trusting the experience. The cause may be visuals, DAX, model shape, DirectQuery, gateway, source performance, or capacity.
The right approach is diagnosis before optimisation. Guessing leads to random changes. Power BI Performance Analyzer, model review, and source checks help identify where the delay actually lives.
The practical context
Use a measured optimisation process for reports used regularly by real users.
Changing DAX or visuals without knowing the bottleneck can waste time.
Report authors own page design and DAX; model owners own structure and refresh.
A faster report with evidence of what improved.
How to approach it
A useful approach is deliberately simple. Start with the business question, make the data and ownership visible, then add technical detail only where it improves reliability or action.
- Open Performance Analyzer and record the slow page.
- Identify whether delay comes from visuals, DAX queries, visual display, or other activity.
- Reduce unnecessary visuals and remove high-cardinality fields from visuals.
- Check model design and prefer a star schema.
- Rewrite expensive measures and test them against realistic filters.
- If using DirectQuery, validate source performance and consider aggregations or Import for summary data.
Common mistakes
Adding more visuals to explain performance problems.
Using one large flat table for every question.
Testing only with small filters.
Ignoring source and gateway performance in DirectQuery reports.
A simple example
A sales dashboard with fifteen visuals may feel slow because every slicer interaction triggers too many queries. Removing low-value visuals can improve experience before any DAX rewrite.
Performance work should leave a record: what was slow, what changed, and what improved.
Checks before you move on
The audience can explain what the output means without the analyst in the room.
The data source, calculation logic, refresh, and access model have owners.
There is a clear path for questions, exceptions, and corrections.
Success is measured by better decisions or less manual effort, not page views alone.
Key takeaway
Power BI performance improves fastest when you find the layer causing the delay before changing the report.
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