Direct-acting antivirals (DAAs) are highly effective, but expensive treatments for chronic hepatitis C (CHC). To manage costs, drug plans worldwide have rationed access to DAAs in a variety of ways. This study quantifies the health impact of formulary restrictions and presents a clinical decision tool for informing treatment timing decisions.A decision-analytic model was developed to quantify the health impact of delaying DAAs for subpopulations stratified by age, fibrosis level, viral genotype, and injection drug use over their lifetime. The health impact was quantified in terms of quality-adjusted life expectancy (quality-adjusted life years, or QALYs) and life expectancy (years).Deferring DAAs for patients with no or mild fibrosis (F0/F1) for 1-5 years is unlikely to result in life expectancy losses and leads only to marginal losses of 0.02-0.06 QALYs per year of delay. However, for 30-50-year-olds with advanced fibrosis (≥F3) delays as short as a year results in a considerable health loss (0.25-1.04 QALYs and 0.19-1.53 years). Reimbursement limits for those with substance use are associated with large health losses. People who actively inject drugs with advanced fibrosis (≥F3) may lose 0.18-1.05 QALYs and 0.13-1.16 years per year of delay, despite the risk of reinfection and competing mortality. Results are robust to parameter uncertainty and key assumptions.We presents a clinical decision tool for informing treatment timing for various CHC subpopulations. In general, findings suggest that patients with at least moderate fibrosis should be treated promptly, regardless of active drug use.