AimTo evaluate whether ≥12‐hr shifts are associated with a decrease in resource use, in terms of care hours per patient day and staffing costs per patient day.BackgroundNurses working long shifts may become less productive and no research has investigated whether potential cost savings are realized.MethodA retrospective longitudinal study using routinely collected data from 32 wards within an English hospital across 3 years (1 April 2012–31 March 2015). There were 24,005 ward‐days. Hierarchical linear mixed models measured the association between the proportion of ≥12‐hr shifts worked on a ward‐day, care hours per patient day and staffing costs per patient day.ResultsCompared with days with no ≥12‐hr shifts, days with between 50% and 75% ≥12‐hr shifts had more care hours per patient day and higher costs (estimate for care hours per patient day: 0.32; 95% CI: 0.28–0.36; estimate for staffing costs per patient day: £8.86; 95% CI: 7.59–10.12).ConclusionsWe did not find reductions in total care hours and costs associated with the use of ≥12‐hr shifts. The reason why mixed shift patterns are associated with increased cost needs further exploration.Implications for Nursing ManagementIncreases in resource use could result in additional costs or loss of productivity for hospitals. Implementation of long shifts should be questioned.