How long can buttermilk stay refrigerated after opening carton?

Buttermilk can typically stay refrigerated for up to 1-2 weeks after opening the carton, but it is always best to refer to the Use By or Best By date listed on the carton for specific information. To maintain freshness and quality, be sure to store the buttermilk in its original container with a tightly closed lid in the coldest part of the refrigerator, usually the back.