While some epidemiologic studies support the hypothesis that stress can adversely affect fertility, few prospective studies have assessed the association in couples from the general population. We used data from Pregnancy Study Online, a web-based preconception cohort study of pregnancy planners from the United States and Canada (2013-2018), to examine the association between women's and men's perceived stress levels prior to conception and fecundability. Women (aged 21-45 years) and their male partners (aged ≥21 years) who were attempting conception without fertility treatment were eligible. We measured perceived stress using the 10-item Perceived Stress Scale (PSS). We ascertained pregnancy information using bimonthly follow-up questionnaires of female participants. We followed 4,769 couples until self-reported pregnancy, initiation of fertility treatment, loss to follow-up, or 12 menstrual cycles of attempt time, whichever came first. We used proportional probabilities regression models to estimate fecundability ratios and 95% confidence intervals, adjusting for potential confounders. Higher PSS scores among the women were associated with slight reductions in fecundability (comparing PSS scores of ≥25 vs. <10, fecundability ratio = 0.87, 95% confidence interval: 0.74, 1.02). PSS scores among the men were not substantially associated with fecundability.