Would this help ?

As my mum thinks im to underweight as it is from my dancing classes and my swimming lessons, she wont let me go out for jogs anymore.
Its horrible because when I eat way to much on my spare days, I have no way of burning it off.
Though my friend told...

me that if you jog on the spot or jog around a room, its just the same as going out for a jog ? ..

So if I jogged on the spot/ around a room for about half an hour
What will this do ?

Hope this helps:

Height and Weights for Teen Girls

Age Range Height Weight Percentile
12-13 years 60 – 63 inches 95 – 105 lbs 50%
14-15 years 63 – 64 inches 105 – 115 lbs 50%
16-17 years 64 inches 115 – 120 lbs 50%
18-20 years 64 inches 125 – 130 lbs 50%

well...ARE YOU underweight? maybe your mom's right to stop you. if you truly are fat and want to jog to stay healthy, then sure, jog in place to your heart's content. if you're underweight like your mom thinks, (and just so you know, she's probably right,) then maybe you should eat a little more food to stay healthy. or if you're willing to go to great lengths to spite your mom, stop jogging, and start eating like a madman! get way fat on her, and then when she tells you to lose weight, you can tell her it's her fault, and she needs to make up her mind about how she wants to run your life. that'll teach her! good luck, either way.

        Simply a Rose to brighten your day,
        And maybe lessen the cares in your way;
        And also, too, to help you to know,
        That in knowing you, many others grow!

 
Check out your BMI at the bmi calculator site below to see where you stand.
 
bmi calculator:

http://www.bmi-calculator.net/

If you need conversion info, 1 kg = 2.2 pounds and 2.54 cm = 1 inch (12 inches = 1 foot)

Info if you are trying to GAIN weight:

http://www.bmi-calculator.net/treatment/underweight-treatment.php

 
Info if you are trying to LOSE weight:

http://www.bmi-calculator.net/treatment/overweight-treatment.php

  
How can I Lose 1 pound of body weight per week?
 
One pound of body fat is equal to about 3500 calories. So to lose 1 pound of weight per week, you need to eat 500 calories/day LESS than you burn.

But it's not a good idea to lose weight simply by cutting calories. As well as decreasing calories you should increase your daily physical exercise. This helps to burn calories and build more lean tissue which in turn burns more calories.

What should a minimum calorie intake be?

As a guide to minimum calorie intake, the American College of Sports Medicine (ACSM) recommends that calorie levels never drop below 1200 calories per day for women or 1800 calories per day for men. Even these calorie levels are quite low.

http://www.bmi-calculator.net/bmr-calculator/harris-benedict-equation/calorie-intake-to-lose-weight.php

 
Average Teenager Weight

http://lifestyle.iloveindia.com/lounge/average-teenager-weight-236.html