Acute-on-chronic liver failure (ACLF) is a rapidly progressive illness with high short-term mortality. Timely liver transplant (LT) may improve survival. We evaluated various indices for assessment of the severity of liver failure and their application for eligibility and timing of living donor LT (LDLT).Altogether 1021 patients were analyzed for the severity and organ failure at admission to determine transplant eligibility and 28 day survival with or without transplant.The ACLF cohort [mean age 44 ± 12.2 years, males 81%) was of sick patients; 55% willing for LT at admission, though 63% of them were ineligible due to sepsis or organ failure. On day 4, recovery in sepsis and/or organ failure led to an improvement in transplant eligibility from 37% at baseline to 63.7%. Delay in LT up to 7 days led to a higher incidence of multiorgan failure (p < 0.01) contributing to 23% of the first week and 55% of all-cause 28-day mortality. In a matched cohort analysis, the actuarial survival with LT (n = 41) and conditional survival in the absence of transplant (n = 191) were comparable, when the condition, i.e., transplant was adjusted. The comparison curve showed differentiation in survival beyond 7 days (p < 0.01).ACLF is a rapidly progressive disease and risk stratification within the first week of hospitalization is needed. 'Emergent LT' should be defined in the first week in the ACLF patients; the transplant window for improving survival in a live donor setting.© 2021. Asian Pacific Association for the Study of the Liver.