The investigators propose to examine whether linking daily activity with charity-based incentives motivates cancer survivors to initiate and maintain physical activity. Linking daily physical activity goals with a cancer specific charity incentive may provide a uniquely salient motivator that promotes increased physical activity among cancer survivors. The investigators will examine whether using activity monitors in combination with charitable incentives leads to greater increases in physical activity compared to activity monitors alone. Target participants includes cancer survivors who are not already active. Physical activity (e.g., steps per day, time in moderate-intensity activity) will be examined at baseline and following a 12-week intervention period using an activPAL accelerometer. After the baseline assessment, both groups will receive a fitbit monitor and informational material designed to increase physical activity. Participants in the fitbit+charity group will have donations made in their name to a cancer charity if they meet daily step goals. Physical activity levels will be monitored using the fitbit device for 6-weeks following the formal intervention period.

The study is a Randomized Controlled Trial (RCT) of a 12-week physical activity intervention. Fifty cancer survivors will be recruited and allocated to one of two research arms: Fitbit+Only Group or Fitbit+Charity Incentives Group. Participants in both intervention arms will be asked to track their physical activities using Fitbit One, an activity monitor that monitors steps and physical activity and will receive basic educational materials about increasing physical activity. Those in the Fitbit+charity incentives Group will raise money for cancer charities if they meet weekly step targets.

The key outcome variable of the RCT is steps as measured by an activPAL accelerometer. Data will be collected at baseline and 12-weeks. Fitbit data will also be collected for the duration of the 12-week intervention and for 6-weeks following the end of the intervention period to have an initial examination of behavior change maintenance (total 18-weeks).

Inclusion Criteria:

1. Adults ≥ 18 years and <50 y, with diagnosed Adolescent or Young Adult cancer (diagnosed between 15-39y of age);
2. ≥ 6 months post-cancer treatment
3. English speaking
4. Participate in <60 minutes of MVPA/week
5. Own a smartphone
6. Have access to computer
7. Participants must also pass a physical activity readiness questionnaire or receive medical clearance from their primary care physician or oncologist.

Exclusion Criteria:

1. Joint, cardiovascular, or respiratory problem(s) precluding physical activity
2. Metastatic disease
3. Planned elective surgery or pregnancy during intervention/follow-up that would interfere with participation (e.g., breast reconstructive surgery).
4. Already using a wearable device >5 days per week