Is it possible to gain 15 pounds of weight from muscle in one year? Last January I weighed 185, and was pretty lean. I have notcied my muscles have grown over the last year and I now weigh 200 pounds. I have eaten right and weight trained at least 3 days per week during the year.

I figure some of the weight is fat, but was % is probably muscle?

Of course! Muscle growth is dependent on a number of factors such as nutritional habits, chronological AND training age (newbies and relative newbies tend to gain muscle much quicker than more experiened lifters, all else being equal), and a healthy endocrine system.

If you happen to be in your teens/early twenties, then this is prime time for growth because of the peak testosterone levels in your body. Provided you get enough protein in your diet, your workouts include most, if not all, of the "big lift" compound exercises such as squats, deadlifts, benchpresses, and pull-ups with their many variations, and you get adequate rest, muscle growth is almost a foregone conclusion.

Yes, it's very possible. Remember, muscle weights more than fat does so you aren't going to get as big gaining 15 pounds of muscle as you probably would gaining 15 pounds of fat. This is why many beleive you should not use a scale to measure progress but rather how you look and feel.

Well that's good news...I was overweight before and seeing weight gain like that freaks me out, eventhough my waist size is still decreasing, and I feel great. I guess I'll keep doing what I'm doing!