This study investigates empirically how net-working-capital (NWC) affects firm value, using a sample of the Vietnamese stock market. Our empirical results indicate an optimal NWC level that maximizes firm value. Our research also shows empirical evidence that deviations from actual and estimated NWC levels (above and below optimal level) can reduce firm value. We show that more than 40% of NWC observations in our sample on the right-hand side of the breakpoint reduce firm value. Managers tend to build up excessive working capital to prevent hiking funding costs after the 2008 crisis. Therefore, our findings help managers determine an optimal level of NWC, which enhances firm value. Our findings are consistent with the trade-off theory.