Background: Mobile health (mHealth) is contributing positively towards HIV prevention for young people across the world. mHealth has the potential to enhance HIV prevention strategies by offering convenient, accessible and private HIV prevention services for young people. However, evidence of knowledge of the usability of mHealth for HIV prevention for young people is limited in South Africa. This study aimed to evaluate the usability and acceptability of a youth-friendly internet-enabled HIV risk calculator for young people, 18–24 years, living in Soweto, South Africa.
Methods: A mixed methods research design study was conducted to collect data through qualitative in-depth interviews and quantitative surveys. Data was collected, analysed and interpreted using a technology acceptance model to answer the research question. A total sample of 129 young women and men aged 18–24 participated in the study, 29 participating in the in-depth interviews and 100 completing the surveys. A semi-structured interview guide was used to collect in-depth information on participants’ perceptions of an internet-enabled youth-friendly HIV risk calculator. Survey data was collected using a demographics questionnaire, and questionnaires on mobile phone usage, substance use, and sexual risk behaviour using REDCap software. HIV testing behaviour, sexual risk behaviour and app usability questionnaires were captured using the HIV risk calculator app through an online link. Qualitative data were analysed through framework analysis using qualitative data analysis software, NVivo version 11 Pro (QSR International). Quantitative data were analysed using quantitative data analysis software, SAS Enterprise Guide 7.1 (SAS Institute, Cary, NC).
Results: Biographical data. The participants’ ages ranged from 18–24, with a median age of 22. Of the 129 participants, 55% were females. All participants were of Black racial descent and unmarried. Most participants (77.9%) identified as straight, 9.8% were gay, 7.4% identified as bisexual, and 3.3% as lesbian.
App usability. In general, the HIV risk calculator (HRC) was acceptable among the participants across the in-depth interviews and survey data. From the survey data, about 98.7% of the participants found the HRC easy to use, and 93.4% thought it would be helpful for their health and well-being. Participants’ overall satisfaction with the HRC app was 97.4%, and 93.4% said they would use the HRC app again.

Mobile phone ownership and usage. Out of 129 participants, 97.7% owned a personal mobile phone, and 60.2% owned a smartphone. The majority of participants who owned a smartphone (97.4%) had access to the internet.
Sexual risk behaviour. Most participants (83.0%) had a sexual partner and just under two-thirds had only one partner as opposed to two or more sexual partners (60.8%). Over half (53.3%) reported changing partners yearly as opposed to weekly or monthly. Just more than two-thirds (72.0%) had typically used condoms with their sexual partner(s). Condom use during the last sexual encounter with a dating partner was 63.6%.
Substance use. Seven (5,4%) participants used marijuana; no other type of drug was reported. Over two-thirds of participants (69.0%) were alcohol drinkers at the time of the study, most of whom drank alcohol sometimes (84.3%). About 56.0% who reported