Standard models of unemployment insurance (UI) focus on how benefit generosity affects the average claim duration, while assuming perfect take-up. Yet, benefit receipt is highly incomplete with estimates of take-up among eligible workers below 50 percent in the United States. In this paper, we show take-up is an important margin of response: If benefits become more generous, more workers claim benefits in addition to claimants remaining on benefits for longer. Using a sample of likely eligible workers, we leverage a regression kink design to identify the causal effect of weekly benefit level on take-up and total benefits paid. Our results suggest a 10 percent increase in the weekly benefit leads to a 4.7 percent increase in take-up, which drives a 6.2 percent increase in total benefits paid. Previous work that focused only on claim duration did not account for this and thus underestimated the fiscal externality from raising benefit levels. These findings have important implications for policy: accounting for endogenous take-up reduces the optimal benefit level by 29 percent and lowers the value of additional spending to raise benefits by 27 percent.