I'm embarrassed to even ask this....

since this topic is SOOOOO popular but "calorie intake vs. calorie output"....?

I am OFFICIALLY in training for the Disney Princess Half Marathon in March.  I have been maintaining my 112 - 115 (5'1", 33 YO F) weight for 6 months now eating between 1500 - 1800 cal/day.  That was with MWF strength training for 30 min and MWF running of between 3 - 5 miles.....

So anyhow, I have stepped up my fitness level to MWF strength training for 30 min, MWF spin classes for 45 minutes, Tues, Thurs run 5+ miles.  Sunday off.  I also just ran my first 15k on Sun (whoo-Hoo!!!, I can do it!!!)So my issue(s) are:  I am VERY worried about gaining.....although I understand it may be inevitable due to the training AND I am very worried that I am not eating enough to sustain this level of activity......I am so new at this and worked so hard to get this 40+ lbs off that I DO NOT want any of it back.  How do I know what is appropriate calorie intake for me at this point?  My main concern is that I remain healthy and do not enter into this "starvation mode" I keep hearing about.  Any thoughts on a "caloric number" that is more in step with my life?

I totally understand how you feel.  What seems to work best for me is slowly upping my calories.  Allow my weight to stablalize, and if I notice I'm gaining, I know I've upped it too much, and cut down a little.  It's a numbers game and you just have to play with it.  If you weigh yourself regularly, you'll have a better understanding of how your body is adjusting.

Good luck with everything!

Punch in your height and weight into c-c.  See what it tells you your daily base burn is.  Add in the calories you burn during your training (look up the activities and punch 'em in with their duration).  The total burn you end up with is how much you need to eat for maintenance.  I'll bet it's a lot more than you have been eating!

Weigh yourself every morning, and dutifully enter the weight here and at the Hacker's Diet website.  Watch the trend.  If it's upward, peel off the computed excess that the Hacker's Diet says you have, and go another week or two.  If it's down, eat more.  If it's level, you're, as Goldilocks said, "Just right."

Don't make adjustments more often than weekly--you need time to average out the daily fluctuations in water and "stuff that's still moving through you" in order to see the trend.

If you're doing all that exercise you're not going to gain.  If you're exercising that much and eating 15-1800 cals/day then you aren't going to have any excess cals to build muscle or fat.

Thanks guys......I appreciate your advice and bpanke, VERY GOOD POINT!  Thanks again!