The advance refunding of debt is a widespread practice in municipal finance. In an advance refunding, municipalities retire callable bonds early and refund them with bonds with lower coupon rates. We find that 85% of all advance refundings occur at a net present value loss, and that the aggregate losses over the past 20 years exceed $15 billion. We explore why municipalities advance refund their debt at loss. Financially constrained municipalities may face pressure to advance refund since it allows them to reduce short‐term cash outflows. We find strong evidence that financial constraints are a major driver of advance refunding activity.