So, teens use more calories than adults, but how much more?

What percentage of the calories adults need do kids need? Is there a way to adapt CC tools to calculate my needs so that I can log exercises? Some days I'm REALLY active. I'm ammorheranic, and I'd like to get it back, which would require eating enough. My doctor has no issues with me exercising as much as I do, but I need to eat enough. He didn't have much insight into how much. Any help, please?

I would suggest using this calculator:

http://www.kidsnutrition.org/bodycomp/bmiz2.h tml

Its commonly recommended on here for people under 21 (:

Decempt got the calculator for under 21s in, as CC's tools won't suit your needs. I also suggest you read this thread on amenorrhoea:  AMENORRHOEA: When You Lose Your Period

Thanks to both of you. One more question....what if I'm active for say, 3 hours on a particular day? Then what do I do?

Some articles that I have read add an average of 50 calories to what an adult's intake would be (with the same weight/height/activity) for growth and development... HOWEVER most calculators do add around 300.

Roughly 300 calories per day more, but kids/teens expend much more energy for the same exertion too so it's better to use the calculator specifically for kids/teens.  It scales according to exercise and growth and is able to give a reasonable determination if BMI is an issue.

http://www.kidsnutrition.org/bodycomp/bmiz2.h tml

Does the calculator have a way of saying how much for 3 hours of exercise? The most that I see is "over an hour" and 3 hours is WAY over an hour.

A heart rate monitor will give you the best info on exercise and calories, otherwise make an estimate by splitting the difference.

An HRM is a bit too much for me, so I'll just estimate...thanks!