The app, called Pact, works by tracking your workouts and awards money if you meet your fitness goals.
The app tracks the users when they check into a known gym and monitors how long they stay.
Users can also wear a fitness band or use their phone's GPS to log miles.
Each week, users pledge that they will do a certain number of workouts. Any gym workout, run, bike ride over 30 minutes, or 10,000 steps in a day counts.
Users also have to enter what penalty they are willing to pay if they miss a workout.
There is a USD 5 minimum fine for skipping a session, 'WFAA-TV' reported.
Reward money is from the pot of fines from people who failed to honour their pact.
Rewards generally range from USD 0.30 to USD 5 per week, depending on the number of activities committed.