How to determine my caloric requirement for a day

I am writing because I am having difficulty determining my caloric needs for each day.  When I use the site's method of calculating, I find it difficult to know if it is accurate.  Changing the amount of activity seems to drastically change my requirement but I don't really feel that I fit well into one of those categories.  I would not call myself sedentary but I do spend the majority of most days sitting as I am a student in class all day and studying most of the evening.  I do however run fairly extensive runs and take part in circuit training classes.  Any suggestion of what to choose for my activity level?  I can't imagine trying to cut my caloric intake to the low 1000's as this seems way too far off from a maintainable lifestyle. 

Incase it helps I am 5"9, weight is 155, and I would like to get to 145. 

Also - if you run 3x per week for example as a habitual thing, if you have called yourself an acitve person do you still add this to the burn meter and therefore give yourself a higher amount to intake for the day???

I really like this site because I think writing my foods down for each day helps me see where I make poor choices and helps me know comparatively how much each food is worth comparatively but I am still struggling to use it in terms of an attempt at a small weight loss.

Any advice? Suggestions?  Sorry for the wordy post, this is my first time posting something :)

Try www.phord.com/cc - it's a calculator that a cc member created that has a different way of defining activity level - seems to work better for those of us who are sedentary and workout.

I use the following:

Step one is to calculate your BMR with the following formula:

Women:
655 + (4.3 x weight in pounds) + (4.7 x height in inches) - (4.7 x age in years)

Men:
66 + (6.3 x weight in pounds) + (12.9 x height in inches) - (6.8 x age in years)

Please note that this formula applies only to adults.

Step two: In order to incorporate activity into your daily caloric needs, do the following calculation:

• If you are sedentary : BMR x 20 percent
• If you are lightly active: BMR x 30 percent
• If you are moderately active (You exercise most days a week.): BMR x 40 percent
• If you are very active (You exercise intensely on a daily basis or for prolonged periods.): BMR x 50 percent
• If you are extra active (You do hard labor or are in athletic training.): BMR x 60 percent

Thanks so much for the quick and helpful replies!  These seem to be more detailed and tailored to the individual which is what I was looking for.  Great to have people out there to help me out!

If I use this system then I work out to 2052.90 ...I"m 5"7 and weigh 310lbs and am 53. So how do I multiply this by 20?

BMR this is the maximum my body needs correct? to lose 2 lbs per week then I need to minus 500 calories per day? so, 1552...how does the sedentry/active thing work into this?

Thanks

Sharron

You want to increase your BMR by 20 percent, so actually you multiply it by 1.2, not 20. In other words, you get 2463.48.

The instructions above are a little off. You should be adding 20 percent not multiplying by 20 percent.

If I get 2463.48 and minus 500 calories per day then I should be eating 1963.98 calories per day? I am presently eating between 1400 and 1800 on what I have considered bad days and still am not losing any weight. I don't understand.

I heard that Christian Bale ate only an apple and drank coffee and cigarrettes to lose weight for his new role in an upcoming film. Obviously he lost the weight in what we would consider a starvation mode, so if I am eating less than 1963.98 calories, how come I am not losing?  Any ideas?

Thanks

Sharron