How long after the expiration date can lactose-free milk be used?

The National Dairy Council says refrigerated milk, including lactose-free milk, can generally be kept 2-3 days past its “sell by” date but notes that some milk producers guarantee their products for longer periods.
 
Some dairy industry experts maintain that it’s best to consume any type of milk before the “sell by” date passes since it’s impossible to know whether the milk was exposed to incorrect temperatures at any stage in the supply chain between the processing plant and the retail cooler. 
 
Source(s):
National Dairy Council Factsheet: “Newer Knowledge of Dairy Foods--Protecting the Quality of Milk and Other Dairy Foods”
Emil Nashed - VP of research and development/quality assurance, Farmland Dairies