According to welfare-maximising principles, the price of parking must vary per day given shifts in daily demand. We study the economic consequences of not doing so by estimating the employees' parking demand at an organisation that varies t h e price of parking by day of the week. We estimate the effect of the employees' parking price on demand using a difference-in-differences methodology. The deadweight loss of free parking due to overconsumption of parking is about 10% of the organisation's parking costs (excluding welfare costs due to increased travel externalities). Charging a fixed price per day induces a welfare loss of at least 4% of the organisation's parking costs.