The exact amount of carbs in a cup of full-fat homemade milk kefir between 1 and 4 grams depending on the fermentation duration.
In milk kefir it is the length of the fermentation process that defines the number of carbs. Typically, the longer fermentation fewer sugars remain in the kefir.
That also reduces the calories in the milk kefir for about 40-50 calories depending on the milk used and fermentation time.