Behavioral: Core The core intervention will include 24 online weekly behavioral modules, an online interactive discussion board, a physical activity tracker, an e-scale with recommendations for daily self-weighing, dietary self-monitoring via an app, as well as weekly calorie and physical activity goals.

Behavioral: Facilitated Weekly Group Sessions Participants will receive 24, 60-minute facilitated online video-conference-based weekly group sessions.

Behavioral: Pre-Scripted Feedback Participants will receive up to 24 weekly messages constructed from a bank of pre-scripted messages that align with success, partial success, or absence of self-monitoring related to diet monitoring, physical activity, and self-weighing, as well as on weekly module engagement.

Behavioral: Individual Coaching Calls Participants will receive 3 30-minute online one-on-one coaching calls to focus on identifying and addressing challenges to successful behavior change and weight loss.

Behavioral: Core The core intervention will include 24 online weekly behavioral modules, an online interactive discussion board, a physical activity tracker, an e-scale with recommendations for daily self-weighing, dietary self-monitoring via an app, as well as weekly calorie and physical activity goals.

Behavioral: Facilitated Weekly Group Sessions Participants will receive 24, 60-minute facilitated online video-conference-based weekly group sessions.

Behavioral: Counselor Crafted Feedback Participants will receive up to 24 weekly messages that are crafted by a trained professional based on their dietary, physical activity, and weight monitoring for the week as well as their completion of online modules, to construct an individualized feedback message.

Behavioral: Core The core intervention will include 24 online weekly behavioral modules, an online interactive discussion board, a physical activity tracker, an e-scale with recommendations for daily self-weighing, dietary self-monitoring via an app, as well as weekly calorie and physical activity goals.

Behavioral: Counselor Crafted Feedback Participants will receive up to 24 weekly messages that are crafted by a trained professional based on their dietary, physical activity, and weight monitoring for the week as well as their completion of online modules, to construct an individualized feedback message.

Behavioral: Individual Coaching Calls Participants will receive 3 30-minute online one-on-one coaching calls to focus on identifying and addressing challenges to successful behavior change and weight loss.

Behavioral: Core The core intervention will include 24 online weekly behavioral modules, an online interactive discussion board, a physical activity tracker, an e-scale with recommendations for daily self-weighing, dietary self-monitoring via an app, as well as weekly calorie and physical activity goals.

Behavioral: Counselor Crafted Feedback Participants will receive up to 24 weekly messages that are crafted by a trained professional based on their dietary, physical activity, and weight monitoring for the week as well as their completion of online modules, to construct an individualized feedback message.

Behavioral: Core The core intervention will include 24 online weekly behavioral modules, an online interactive discussion board, a physical activity tracker, an e-scale with recommendations for daily self-weighing, dietary self-monitoring via an app, as well as weekly calorie and physical activity goals.

Behavioral: Pre-Scripted Feedback Participants will receive up to 24 weekly messages constructed from a bank of pre-scripted messages that align with success, partial success, or absence of self-monitoring related to diet monitoring, physical activity, and self-weighing, as well as on weekly module engagement.

Behavioral: Individual Coaching Calls Participants will receive 3 30-minute online one-on-one coaching calls to focus on identifying and addressing challenges to successful behavior change and weight loss.

Behavioral: Core The core intervention will include 24 online weekly behavioral modules, an online interactive discussion board, a physical activity tracker, an e-scale with recommendations for daily self-weighing, dietary self-monitoring via an app, as well as weekly calorie and physical activity goals.

Behavioral: Pre-Scripted Feedback Participants will receive up to 24 weekly messages constructed from a bank of pre-scripted messages that align with success, partial success, or absence of self-monitoring related to diet monitoring, physical activity, and self-weighing, as well as on weekly module engagement.

Participants will receive 24 facilitated online video-conference-based weekly group sessions. These groups will be 60 minutes long and will be facilitated by a trained professional, who reinforces the information and behavioral strategies introduced in the weekly modules, elicits the experiences of participants in applying behavioral skills to establish new diet and exercise habits, and guides problem solving. Group cohesion to offer social support is promoted.

Participants will receive up to 24 weekly messages that are crafted by a trained professional based on their dietary, physical activity, and weight monitoring for the week as well as their completion of online modules, to construct an individualized feedback message. The emailed feedback will provide positive reinforcement for successful goal achievement, identify possible areas for improvement, and suggest possible strategies for identified challenges.

Participants will receive 3 online one-on-one coaching calls to focus on identifying and addressing challenges to successful behavior change and weight loss. The first call will emphasize amplifying motivation and promoting early treatment engagement by establishing rapport, exploring personal reasons for weight loss and lifestyle change, and reinforcing and expanding change talk, and it will occur prior to starting the core program. Subsequent calls will use a motivational interviewing-informed approach to problem solve barriers to self-monitoring, particularly dietary self-monitoring because of the strong role it plays in promoting better weight loss and will occur during the first half of the program, reflecting the critical role of early engagement in the treatment program on long term weight loss success. Coaching calls will be of approximately 30 min duration and will follow a semi-structured interview format.

Participants will receive up to 24 weekly messages constructed from a bank of pre-scripted messages that align with success, partial success, or absence of self-monitoring within each of the following domains: dietary monitoring, physical activity monitoring, and self-weighing, as well as on weekly module completion. Feedback is automatically generated based on decision algorithms and will be sent from program staff.

Dietary self-monitoring will be objectively measured as the number of days on which data on dietary intake (foods and beverages consumed) for a minimum of 2 meals were entered into the Fitbit app and transmitted to the study team via Fitbit API

physical activity self-monitoring will be objectively measured as the number of days on which activity data were collected by wearing the study-provided Fitbit tracker and were transmitted to the study team via Fitbit API; days with wear time of a minimum of >/= 10 hours, assessed as 10 hours of non-zero heart rate measurements captured by the Fitbit device, will be considered as a day of self monitoring

The proportion of modules presenting behavioral weight management skill building lessons which are completed by participants will be determined through website utilization data and proportion completed will be calculated as number of modules completed / 24 [i.e., the total number of modules made available over the course of the intervention]

Attendance at treatment sessions will be recorded by interventionist personnel delivering the sessions for those participants randomized to receive these treatment elements and the proportion attended will be calculated (attended /number offered).

Self-regulation is the general ability to regulate behavior to achieve desired future outcomes and personal goals through monitoring progress through self-monitoring, goal setting, getting feedback, making adjustments to behavior, and self-rewarding; utilization of weight management self regulation processes will be assessed using the Self-Regulation Questionnaire (Kliemann, Beeken, Wardle, 2016). The measure has 63 items which are answered on a 5-point Likert scale (1-strongly disagree top 5= strong agree) and higher scores indicate a greater-self-regulation capacity.

Supportive accountability may increase treatment adherence when a trustworthy and caring person with specific expertise is perceived to be monitoring one's actions, and individuals feel an obligation to deliver on a commitment or explain reasons for failing to achieve an outcome. The investigators will assess supportive accountability using the Support Accountability Inventory (Meyerhoff, Haldar, & Mohr, 2021). This inventory consists of 6 items with a Likert scale response format ranging from 1 (Strongly Disagree) to 7 (Strongly Agree), with higher total scores indicating higher perceived supportive accountability

Problem solving is a formal process to identify barriers and challenges to behavior change and constructively identify potential resolutions to minimize the negative impact of the barriers on behavior change; problem solving will be assessed by the Problem Solving Test (Nezu, Nezu & D'Zurilla, 2012)

Autonomous reasons for engaging in weight control efforts (personal reasons for change or motivations that reflect an internalized rationale for change) and controlled motivation reasons for behavior change and weight loss that are externally imposed or arise from others) will be assessed with the Treatment Self-Regulation Questionnaire (Williams et al, 1996). The measure consists of 12 items, all scored using a 7-point Likert scale (1= not at all true to 7 = very true). Higher scores on the Autonomous Subscale (6 items) indicate greater autonomous motivations for behavior change and higher scores on the Controlled Motivations subscale (6 items) indicate higher controlled regulation.

Social support can facilitate weight loss and a group based program such as this can offer social support, assessed by the Social Support for Healthy Behaviors Scale which queries about social support for and sabotage of weight control behaviors from family, friends, and group members. Eighteen items assess support/sabotage for consuming a healthy dietary pattern over the previous month (the same 9 items rated separately for family members and for friends/group members using response options on a 4-point scale which ranges from almost never to almost always). Responses are coded into a social support subscale and a sabotage subscale, with higher mean scores indicating more support or more sabotage, respectively. An additional 18 items assess social support/sabotage for physical activity from family and friends using the same format (Ball & Crawford, 2006; Kiernan et al, 2012)

Perceived social support and group cohesion may differ based on whether individuals participate in synchronous face-to-face group sessions or if they have asynchronous, text-based communication to offer social support; therefore, we will assess group cohesion using the Group Cohesion Scale (Procidano &Heller 1983). This measure has 20 items focused on perceptions of other group members which employ a yes/no answer format plus a rating of perceived support from group leader item which ranges from 1 to 10 (with 10 being extremely supportive and 1 being not at all supportive). Higher total scores indicate greater perceived cohesion and social support from the group.

The non-research related costs associated with delivery of each treatment component will be continuously monitored.

Perceived accountability will be assessed using the Perceptions of Accountability subscale of the Supportive Accountability Measure (Chhabria, Ross & Leahey, 2020). This measure includes 10 items, using a 7-point Likert scale (1 = not at all to 7 i= very much). The minimum score obtainable is 10 and the highest possible score is 70, and higher scores indicate greater perceived accountability.