Background: In 2009, mandatory folic acid fortification of bread-making flour was introduced in Australia to reduce the birth prevalence of preventable neural tube defects (NTDs) such as spina bifida. Before the introduction of the policy, modelling predicted a reduction of 14–49 NTDs each year. Objective: Using real-world data, this study provides the first ex-post evaluation of the cost effectiveness of mandatory folic acid fortification of bread-making flour in Australia. Methods: We developed a decision tree model to compare different fortification strategies and used registry data to quantify the change in NTD rates due to the policy. We adopted a societal perspective that included costs to industry and government as well as healthcare and broader societal costs. Results: We found 32 fewer NTDs per year in the post-mandatory folic acid fortification period. Mandatory folic acid fortification improved health outcomes and was highly cost effective because of the low intervention cost. The policy demonstrated improved equity in outcomes, particularly in birth prevalence of NTDs in births from teenage and indigenous mothers. Conclusions: This study calculated the value of mandatory folic acid fortification using real-world registry data and demonstrated that the attained benefit was comparable to the modelled expected benefits. Mandatory folic acid fortification (in addition to policies including advice on supplementation and education) improved equity in certain populations and was effective and highly cost effective for the Australian population.