Depending on the type of loan it is either 1/4 or 1/8 of a percent. Some lenders will err on the side of caution and use the 1/8 of a percent change on all loans no matter what loan product is used in the transaction.
In unofficial guidance, CFPB Director Richard Cordray has stated that the CFPB will only be concerned about changes that increase the APR by the stated limits. Despite this guidance, lenders may remain cautious and require a new three-day review period for decreases in APR as well.