Now that you have finally committed to a regular exercise schedule, you hesitate taking a break from it. You should remember though that resting is important for two reasons:
1. If you do primarily cardio, you are depleting your muscles. You probably feel tired and need a little motivation to get to the gym. This is because your muscles need some rest.
2. If you do weight training, you are tearing muscle tissue. If you want to build up muscle you need to give your muscles time to recover.
How much should one rest? You should probably do cardio only 5 out of the 7 days. As for weight training, you should work out different muscle groups each time so that you give them time to recover in between training sessions.
Bonus: Take a day off from working out during the week. This will feel like a real treat, especially if you tend to stress out about school, homework, work or other engagements. Choose which day is the most difficult for you, and allow your body to rest. You can work out a little extra hard during the weekend!