Question: When is the Last Day to Use American Express Costco Credit Card?
Answer: The last day to use American Express Costco Credit Card was June 19, 2016. One June 20, 2016 Costco switched to Visa for processing its credit cards. After June 20, 2016 you are no longer able to use your American Express Costco TrueEarning Credit Card.
From June 20, 2016 and afterward, Costco only accepts Visa Credit Cards in its stores.