How do levels of cognitive household labor — the ``mental load’‘ involved in anticipating, fulfilling, and monitoring household needs — affect political engagement? The mental load is distinct from the physical tasks of e.g., cooking and cleaning, and thought to be disproportionately undertaken by women. Thus far, the few studies addressing the issue have used qualitative methods to document it, and the topic has yet to be studied in political science research. As a result, we may be underestimating household gender gaps and their impact on politics. To investigate this question, I field a descriptive survey on politics and household work to parents in the United States. My survey’s novel approach uses a series of questions that ask about who in the household does different cognitive labor tasks. I argue that women have higher mental loads than men, and large mental loads decrease political interest for women. I find support for this theory: women report being mostly responsible for 70 percent of cognitive household labor, while men report being mostly responsible for 30 percent. This 40 percent gender gap is twice as large as the gender gap in physical household labor, and it persists across a range of characteristics. Additionally, I find that the mental load moderates the relationship between gender and political interest, with women, but not men, reporting less interest in politics as the mental load increases. Taken together, my findings offer new empirical evidence about a gender gap too often hidden, and its consequences for equality in democratic life.