Haupert, Gesselman, Moors, Fisher and Garcia’s 2017 study in the Journal of Sex & Marital Therapy, drawing on two nationally representative samples of single US adults (combined N=8,718), found that 21.9% in Study 1 and 21.2% in Study 2 reported engaging in consensual non-monogamy at some point in their lifetime, with the proportion stable across age, education, income, religion, region, political affiliation, and race. This 21% lifetime-engagement figure is used here as a revealed-preference floor on the inaction-side regret rate: at least this share of the US adult population has actually engaged in CNM, which traces a lower bound on the share of strictly-monogamous adults who would regret never having tried. The underlying pool of regret-curious-but-never-engaged adults — those constrained by partner agreement, social cost, or default inertia — is necessarily larger. No survey directly asks long-term monogamous adults “do you regret never having tried opening?”, so the 21% revealed-preference rate substitutes for the missing regret item. The OPEN 2025 Community Survey, conducted under Chapman University IRB by Dr. Amy Moors with 5,885 respondents from 65 countries, indicates that the CNM-identified population has grown substantially since the Haupert 2017 fieldwork, so the 21% should be treated as a conservative lower bound on current regret-curious population.
The action side — adults who opened their relationship and regret having done so — is the harder side to estimate. Conley, Matsick, Moors and Ziegler’s 2017 review in Perspectives on Psychological Science (PMID 28346120) synthesizes the comparative literature and finds few differences in relationship functioning between monogamous and CNM individuals. Conley, Piemonte, Gusakova and Rubin’s 2018 study in the Journal of Social and Personal Relationships reports that monogamous people report slightly lower sexual satisfaction and lower orgasm rates than CNM individuals, with swingers reporting higher sexual satisfaction than monogamous individuals and those in open relationships reporting equivalent satisfaction; relationship satisfaction did not differ between groups. Satisfaction parity is not the same as low regret, but it bounds the regret rate: if the average CNM participant reports satisfaction comparable to the average monogamous person, the lifetime-regret share among opened adults cannot be dramatically higher than the monogamy baseline. The 15% shown on the action side is not a measured or derived regret rate — it is a display placeholder pinned to that satisfaction-parity bound, because no survey directly asks opened adults whether they regret the decision. The cross-sectional satisfaction samples also partly miss the elevated dissolution rate during the opening transition itself, since dissolved CNM-attempting couples are absent from the currently-in-CNM populations, so even the parity bound is read loosely.
The directional finding — inaction-side regret modestly exceeds action-side regret — is consistent with Roese and Summerville’s 2005 meta-analysis of 11 regret-ranking datasets, which identifies romance as the third-largest lifetime regret domain (14.8%) and finds inaction regrets persist longer than action regrets because they reflect greater perceived opportunity. A long-term monogamous adult who was curious about CNM but never explored falls squarely in the missed-opportunity-in-romance pattern. The delta is small (6 percentage points) and should be held loosely on magnitude: both rates are proxy constructions, the action-side rate is particularly speculative because no survey separates opened-and-stayed-open adults from opened-and-closed-again adults, and the published CNM-satisfaction literature faces non-trivial publication and researcher bias in both directions (Conley et al. document that polyamory-favorable findings face more bias accusations, while the field is dominated by CNM-sympathetic researchers). The r/OpenMarriageRegret subreddit with 16,000+ members is sometimes cited as evidence of high action-side regret; we have not used it because it is a self-selected community with no denominator. The 21%/15% rates are US-adult averages and do not generalize cleanly across gendered or orientation gradients — Haupert found higher CNM engagement among men and LGB respondents, so the regret-curious population is itself gendered.