Question

Why is my DAX measure returning incorrect results for calculated totals, even though row-level calculations are correct?

In some cases, a DAX measure may calculate row-level values correctly but return inaccurate totals. Why might this happen, and how can DAX formulas be adjusted to ensure that totals are computed correctly across all rows?

Answer 1

• It is quite common for DAX measures in Power BI to produce incorrect totals, although they may perform correctly for row-level calculations. This phenomenon usually happens because the interpretation of totals in DAX is inconsistent with row-wise calculations. More specifically, DAX totals are often not even close to the simple math of summing individual calculations – rather, totals are taken from the results over all rows or some of the rows, but not necessarily adding the individual calculations together. In fact, totals quite often utilize the entire table or pertinent carried-over measure context, which can lead to surprises if the measure definition is not modified to fit that larger picture.

• One reason for this is how DAX differentiates between row context and filter context. Row-level calculations are usually confined within the row context, and they assess each row separately. However, when summing up a measure, DAX provides a filter context that includes all available rows under the specified filter. Unless the DAX expression is carefully designed to incorporate this difference, the total value of the measure will differ from what was intended.

• In such cases, you can often modify the DAX formula to specify the total to be computed in the desired way. For example, including the SUMX, AVERAGEX, or CALCULATE functions in your measure will make sure that aggregation is done after invoking the measure on each row. Also, SUMX allows for greater manipulation of the grand’s total as it calculates the given expression to each row of the entered table and adds the results. With such functions incorporated in the preparation of DAX measures, one can bring about the total calculation that corresponds with the calculation meant for each row, making all rows give the correct results.

Answer 2

It mostly happens due to the sensitivity of a DAX measure towards context with reference to which it is being ensured to be calculated. The row-level calculations might be correct logically, but they won't tally up into a total because of its DAX method of aggregating values across multiple rows.

This means using CALCULATE with filtering or actually using SUMX to iterate over a table instead of summing results directly. Be careful of any context transition problems, especially for filter expressions whose evaluation may differ at row and total levels. Remove those unwanted filters while calculating the total by using the ALL or ALL EXCEPT functions.