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PURPOSE Contact days exceeding trial protocol–mandated care may represent adverse clinical events and portend worse outcomes. Identifying patients at risk of poor outcomes could enable clinical teams to intervene early and support patients' needs. MATERIALS AND METHODS We linked data from 6 SWOG trials to Medicare claims. We calculated contact days (days with ambulatory, emergency department, inpatient, or facility-based care) and their composition using protocol calendars. Total contact days were delineated as protocol-mandated (planned) ambulatory or unplanned (including unplanned ambulatory v unplanned inpatient). Cox frailty landmark regression analysis was used in a random 60% training set to identify the optimal threshold (percentile) and landmark (months) for contact-day measures as the predictor based on the chi-square statistic. Candidate predictors were tested in the remaining 40% sample. RESULTS We included 1,429 patients (median age, 71 years, 7.6% Black, 21.4% female). In the first 3 months, among 15,301 contact days in the training set (6.4 contact days per person per month; 21.2% of total days), 4,102 (26.8%) were protocol-mandated ambulatory, and 11,199 (73.2%) were unplanned (including 7,328 [47.9%] ambulatory and 3,871 [25.3%] inpatient). The 2-month follow-up time at the 75th percentile threshold was the optimal model in the training set. In the test set, unplanned contact days, especially unplanned inpatient contact days, were associated with subsequent survival (≥1 unplanned inpatient contact days, adjusted hazard ratio, 1.25 [1.02-1.52], P = .014). CONCLUSION One in five trial follow-up days was a health care contact day, of which the majority were unplanned ambulatory contact days. Meaningfully decreasing contact-day burdens will require addressing uncoordinated unplanned ambulatory contact days. The low threshold (≥1 in the first 2 months) of unplanned inpatient days in predicting mortality highlights the adverse impact of any acute care use on survival.