So much affects how you burn calories--more than just your age, current weight, and gender affect metabolism.
Pages like this one provide a very rough sort of estimate of calories needed to maintain weight, and you could view the info on the page as a good starting point and make adjustments from there:
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Personally, I tend to think that this (caloric intake) tends to be a unique thing. My calorie intake goals are dynamic--they change as I age, and as my metabolism and activity levels shift around. And sometimes, they change because some other factors vary--for example, when I am under a lot of stress, I burn many more calories. Because of all of these things, I make adjustments along the way. No way do I have a static formula for calories in/out.
