DAX function

KEEPFILTERS — DAX function reference

Add a filter without overriding.

Syntax

dax

CALCULATE(<expression>, KEEPFILTERS(<filter>))

dax

CALCULATE([Sales], KEEPFILTERS(Sales[Region] = "West"))

→ A number

Without KEEPFILTERS, every row of a category-sliced visual would show the Bikes total because the boolean filter overrides the existing context.

dax

CALCULATE(SUM(Sales[Amount]), KEEPFILTERS(Product[Category] = "Bikes"))

→ Only returns a value for Bikes; other categories return blank

dax

CALCULATE(SUM(Sales[Amount]), KEEPFILTERS(Sales[Amount] > 500))

→ Combines with any existing amount filter instead of overriding it

Intersects with existing context instead of replacing it.
Normally a CALCULATE filter argument overrides existing context on the same column; KEEPFILTERS intersects (ANDs) with it instead — the visible symptom of forgetting it is a matrix where every row shows an identical total.
KEEPFILTERS has no effect when there's no pre-existing filter on that column to intersect with — it doesn't change results unless the filter it wraps overlaps existing context.

From Filter context