doi:10.1108/JSTP-05-2021-0084engMinguez Penalva, A.Sese Oliván, F. J.How does relationship length influence donation amount over time for regular members of nonprofit organizations – the moderating role of donation frequencyART-2022-129179Purpose: The purpose of this study is to investigate whether a U-shaped relationship exists between the length of time a donor has been a regular member in a nonprofit organization and the amount donated over time. In addition, this research analyzes whether this relationship is moderated by donation frequency. Design/methodology/approach: Using a database of 6, 137 members from a collaborating nonprofit organization, a longitudinal study is conducted over an eight-year period (2013–2020). A set of ordinary least square (OLS) regression analyses are carried out to empirically test the proposed hypotheses. Findings: This study finds a nonlinear, U-shaped relationship between donation amount and relationship length. This effect can be explained through the dynamic evolution of two dimensions of commitment: affective (decreasing over time) and normative (increasing over time). The results also reveal that these effects, however, become flatter for members who engage in more frequent donations. Originality/value: The results provide novel insights revealing the nonlinear nature of the relationship between the length of time a donor has been a member of a nonprofit organization and the amount donated, and underscores the moderating role of donation frequency, which makes the U-shaped relationship flatter, thus increasing the amounts donated. Despite their relevance in the service ecosystem, nonprofits have been under-represented in prior work. This study offers important practical insights into the effective management of the regular donor portfolio. © 2022, Emerald Publishing Limited.2022http://zaguan.unizar.es/record/14846210.1108/JSTP-05-2021-0084http://zaguan.unizar.es/record/148462oai:zaguan.unizar.es:148462info:eu-repo/grantAgreement/ES/MICINN-FEDER/ECO2017-83993-PJournal of Service Theory and Practice 32, 3 (2022), 432-451by-nchttp://creativecommons.org/licenses/by-nc/3.0/es/info:eu-repo/semantics/openAccess