You can stay fit by exercising at home. It doesn't take much to get fit. You can perform simple exercises at your home without needing expensive equipment.
You just need to have a pair of dumbbells, a mat, a chair, and a timer.
The most important thing is ensuring you are consistent with your workouts. You could lose motivation if your workouts are not consistent for more than a few consecutive days.
A great way to start off would be to try lifting weights three times per week. This could include push-ups/pullups/squats/lunges, pushups/pullups, dips/curls, and so on.
Once you have mastered the basic movements, it is possible to move on to other types such as running and jumping rope, skipping or yoga, Pilates, dance, swimming, weight lifting, tennis, golf, playing basketball, soccer, volleyball, badminton or squash.
Make sure you choose the right exercise program for your needs. Avoid exercises that demand too much energy if you work long hours.
If you are a night person, it's a good idea to work out during the evening rather that in the morning.
Listen to your body. Stop when you feel tired.