In a Black and Scholes (1973) world, this paper studies the pricing performance of a closed‐form lower bound to American option values based on an exercise strategy corresponding to a flat‐exercise boundary. The lower bound has a simple two‐step implementation akin to Barone‐Adesi and Whaley (1987) formula and shows superior pricing performance in the out‐of‐the‐money region and for long maturities.