The present study advances a within-person approach to the study of workaholism in line with whole trait theory, arguing that individuals have general workaholic tendencies as well as daily fluctuations in workaholism. We tested this model using an experience sampling study of 121 U.S. employees and their spouses who completed self-report surveys for 10 working days. Multilevel analyses supported the idea that workaholism varies at the daily level, and trait workaholism was significantly related to higher daily fluctuations in workaholism averaged across the 10 days. Consistent with whole trait theory (Fleeson, 2007), we found anticipated workload each morning positively related to daily fluctuations in workaholism. Moreover, individuals reported feeling more fatigued on days they report higher daily workaholism, and daily fluctuations in workaholism were related to stress crossover and spouse's relationship tension. Overall, results support a within-person conceptualization of workaholism, linking anticipated workload to daily fluctuations in workaholism, which in turn demonstrates negative spillover and crossover outcomes. (PsycInfo Database Record (c) 2021 APA, all rights reserved).