Inclusion Criteria:  Patients ≥ 13 and ≤ 30 years old with a history of HSCT of any type, at least 100 days post-transplant at initial consultation of the study, will be eligible for the study. Both male and female patients will be eligible. Patients must classify as obese, represented as Body mass index [BMI] ≥85th percentile for age and gender. Patients must also be able to read English since the app intervention is only available in English form.  Exclusion Criteria:  Patients who are ≤ 13 or ≥ 30 years old are not eligible for the study. Patients who are < 100 days post-transplant at initial consultation will not be eligible for the study, but may become eligible if they are >100 days post-transplant at their next consultation that falls within the enrollment window. Patients whose BMI does not fall under the obese category will be excluded. No patients will be excluded for any specific underlying medical condition, but decisions will be made on a case by case basis if a patient's functioning is deemed to significantly interfere with intervention participation.