Why is the Power BI report slow?

Slowness is perceived as a reporting issue, but it is almost always a model issue. Four causes account for most cases.

The model contains more than it needs

All columns were included because that was easiest. Columns with many unique values—especially free text and timestamps with second-level precision—are disproportionately costly. Removing what you do not use is the simplest and most effective measure.

DirectQuery Where Import Would Have Sufficed

Every action queries the source system. If real-time data is not a genuine requirement, Import delivers an immediately noticeable improvement.

Resource-intensive calculations that run for each row

Calculations that need to process the entire table for each view become costly as the amount of data grows. They can often be rewritten or moved to where the data is loaded.

Too much on one page

Each visualization is a separate query. Twenty elements on a page means twenty queries every time someone changes a filter. Split them across multiple pages.