muscle mass and daily calories?

Hi all, I'm wondering about how your amount of muscle mass affects calories per day.

A couple of years ago I got down from 200 to 165, and I'm now really wanting to lose that last 20 pounds. I'm 5' 6'' and Fitday says I should be at 1280 calories net a day in order to have a 500-calorie per day deficit. But I'm finding that I'm quite hungry a lot of the time and also kind of dizzy by the end of the day, particularly just before dinner. I do five or six 40-minutes cardio workouts per week and lift weights several times a week as well, but I make sure to eat back those calories.

So anyway, I'm wondering if maybe my amount of muscle mass could mean I'm burning more calories per day that Fitday thinks?

I think I probably have a good amount of muscle mass because 1) I've been working out intensely for about 5 years and have really strong legs in particular (I can leg press 350 for 3x10 reps). 2) when I got down to my current weight a few years ago, I noticed that at the end of my process I went down a half-size without weighing any less, which suggests to me I was maybe adding muscle while losing fat.

So maybe I'm burning more calories than Fitday thinks? Or maybe I'm not eating the *right* 1280 calories (should I try more protein??)? Or maybe I'm just fooling myself because I want to eat more? :-)

I am hoping I don't have to splurge on a fitbit to find out the answer!!

Thanks for any advice!!

PS Forgot to say I'm 42!