What is DAX?

DAX is the language you use to write calculations. Simple measures such as sums and averages resemble Excel so closely that people are fooled into thinking the rest does too.

The big difference

In Excel, a formula calculates based on the cells you reference. In DAX, a measure calculates based on what is filtered at the point where the measure is displayed. The same measure produces different values in different parts of the report, and that is intentional. This context is both its strength and the most common source of confusion.

What is worth learning first

Start with the simple aggregations, then master one function: the one that lets you change the filter context in which a calculation runs. With that in place, you can cover most of what the business asks for.

When things get confusing

If the formulas become long and difficult to explain, the problem is usually the model, not your DAX knowledge. Complex calculations are often a sign that the tables should have been structured differently.