Background: Micronutrient inadequacies are estimated to affect billions of people worldwide, yet these estimates exclude fortification. There are no global estimates of the impact of current fortification programs on micronutrient inadequacies. Current fortification standards, compliance, and coverage is also suboptimal, with room for significant improvements. Methods: We estimated the prevalence of inadequate intakes for 13 essential micronutrients across 185 countries by integrating global modelled dietary intake data with fortification program parameters. We modelled six scenarios: no fortification, current fortification, improved compliance, aligned standards, aligned standards with improved compliance, and expanded coverage. Implementation costs were calculated as the sum of premix, industry-related, and government costs across five commonly fortified food vehicles: wheat flour, maize flour, oil, rice, and salt. Findings: Relative to no fortification, current fortification programs prevent 7.0 billion inadequate person-nutrient intakes annually at a global cost of $1.06 billion ($0.18 per person), with iodine fortification alone preventing 3.3 billion inadequacies. Despite these efforts, 38.6 billion inadequacies persist. Improving compliance would prevent 13.1 billion inadequacies at $3.48 billion annually ($0.23 per person). Aligning standards and improving compliance would prevent 17.2 billion inadequacies at $6.6 billion annually ($0.63 per person). The most comprehensive scenario—aligning standards, improving compliance, and expanding coverage—would prevent 24.7 billion inadequacies at $9.2 billion annually ($1.15 per person), though 20.9 billion inadequacies would remain. Interpretation: Fortification is a cost-effective intervention that significantly reduces micronutrient inadequacies, particularly for iodine and iron. Prioritizing improved compliance with existing standards offers the most immediate gains, while alignment with international guidelines and program expansion could triple impact. However, even optimal fortification cannot eliminate all inadequacies and carries some risks for excessive intakes, underscoring the importance of complementary approaches to achieve healthy diets for all.