This paper examines the impact of constitutional rules on parliamentary dissolution, government termination and duration with a particular focus on the likely effects of UK’s Fixed-term Parliament’s Act (2011). In the UK debate, expectations about the Act diverge. This article evaluates the plausibility of these contrasting views by combining evidence from a comparative analysis of European cabinets with a counterfactual analysis of the Act’s effect on the strategies of UK politicians. The evidence from both analyses indicates that fixing the term of parliament is likely to render parliaments more stable, but may also have the unanticipated effect of making governments more vulnerable to failure and replacement.