ObjectivesTo assess delays to antiretroviral therapy (ART) initiation before and after the Universal Test and Treat (UTT) and the same-day initiation (SDI) of ART policy periods in Johannesburg, South Africa.DesignProspective cohort study.SettingPatients were recruited from six primary health clinics in Johannesburg.ParticipantsOverall, 1029 newly diagnosed HIV positive adults (≥18 years) were consecutively enrolled by referral from the testing counsellor between April and December 2015 (pre-UTT n=146), July and August 2017 (UTT, n=141) and October 2017 and August 2018 (SDI, n=742).Main outcome measuresCox proportional hazards regression was used to assess predictors of 30 days ART initiation. Additionally, predictors of immediate ART initiation were evaluated using Poisson regression.ResultsOverall, 30 days ART proportions were 71.9% overall, 36.9% pre-UTT (44.3% of those eligible), 65.9% under UTT and 79.9% under the SDI policy. The median days to ART initiation declined from 21 pre-UTT (IQR: 15–30) to 8 (IQR: 6–16) under UTT and 5 days (IQR: 0–8) under the SDI policy. However, only 150 (20.2%) of the SDI cohort-initiated ART immediately after HIV diagnosis. Living in a two-adult home (adjusted HR (aHR) 1.2 vs living alone, 95% CI 1.0 to 1.5) increased the likelihood of 30-day ART. Missing baseline cluster of differentiation four (CD4) data decreased the likelihood of 30 days ART by 40% (aHR 0.6 vs CD4 <350 cells/µL, 95% CI 0.5 to 0.7). More women took up immediate ART (adjusted relative risk (aRR) 1.3, 95% CI 1.0 to 1.9). Participants ≥40 years (aRR 0.6 vs 18–24 years, 95% CI 0.4 to 0.9) were less likely to start ART immediately after HIV diagnosis. However, immediate ART rates increased with longer policy implementation time (aRR 0.2 for <3 months vs >10 months, 95% CI 0.1 to 0.4).ConclusionsThe study results highlight a positive move towards earlier ART initiation during the UTT and SDI periods and emphasise a need to increase same-day ART implementation further.