Background <p>Methods for the economic evaluation of implementation initiatives to increase the uptake of cost-effective healthcare interventions are not standardised. Value of implementation and policy cost-effectiveness are two proposed approaches. This research aims to compare these two methods and propose a standardised approach. To illustrate this, we evaluated two implementation programmes to increase magnesium sulphate (MgSO₄) uptake in preterm labour to reduce the risk of cerebral palsy: (i) the National PReCePT Programme (NPP), which provided regional support and funded clinical time in maternity units in England, and (ii) an enhanced support programme (ESP) with additional unit-level coaching and extra funded time, which was nested within the NPP and subject to a cluster randomised control trial.</p> Methods <p>After summarising value of implementation and policy cost-effectiveness methods, we explored the extent to which the two methods can be viewed as mathematically equivalent for the purpose of evaluating the NPP (versus pre-existing trends) and the ESP (versus the NPP) calculating their incremental cost-effectiveness ratios, net monetary benefits and their probability of being cost-effective.</p> Results <p>We demonstrate how the value of implementation and policy cost-effectiveness approaches can be expressed in equivalent terms and set out our standardised stepwise method for evaluating the NPP (versus pre-existing trends) and the ESP (versus the NPP). Our method found that the NPP generated a net monetary benefit of £30,247 per maternity unit over 12 months, with a 98% probability of being cost-effective. In contrast, the ESP generated a net monetary loss of £28,682 per unit compared with the NPP, with a 22% probability of being cost-effective.</p> Discussion <p>Our standardised method could promote a more systematic assessment of the value for money of implementation interventions.</p>