The good news is that when i originally came up with the number i must have either been using a lower weight or a going by the RMR number, because my BMR doesn't go south of 1800 calories per day until i hit 175, though the RMR would be down to 1725 at that point. I think i'm content with sticking with 1800 for now. When/if i hit 175 i can consider dropping 100 calories, which would be good until i got south of 160, or i could just accept a slightly lower weight loss rate.
I was wondering what my activity factor was though, and decided to follow their advice and use one of the other calculators to actually figure out how many calories i burn in a normal day. The results were weird.
For a normal work day, mostly just sitting and using the computer, my total calories came out to 2651 (when calculated at 180 lbs, slightly lower than i am now.) My BMR/RMR at that weight is 1828/1748, so that would correspond to an activity level of almost 1.55, which they describe as "Moderately Active" and "Moderate exercise or sports 3-5 days a week." Which i get to just by sitting at a desk all day.
They do acknowledge at the bottom of the page that there are issues with the way BMR and RMR are calculated that cause them not to align with specific measurements of activity, but that seems a little extreme.
It also seemed somewhat extreme that just by sitting at a desk i was burning a little more than 851 calories per day over what i was consuming.
So i did some more math. I constructed several different sample days; work days, weekends, clubbing, climbing, rollerblading, and various combinations therein. On the low end, my lazy weekend days burn 2314 calories. On the high end, for the once a month days where i go to work and then go to Wumpskate afterwards i burn 3519. (Though i'm slightly suspicious of their number for rollerblading and wonder if perhaps that's 200-400 calories too high.)
I then constructed a virtual month and averaged it out. That average came to 2796 per day. First conclusion, my current exercise regimen doesn't raise the average over a work day that much, perhaps i should be exercising more =P
However that means in theory i'm losing 996 calories a day, which sounded like a lot till i did some more math. At 3500 calories per pound of fat that means that in theory i'm losing 0.28 lbs of fat a day, and for the 58 days i've been going so far i should have lost 16.5 lbs. In actuality i've lost 14 lbs so far. However given that i'm not perfect about measuring my calorie intake and i do allow myself to splurge once in awhile that probably actually tracks pretty close to reality. Although on the other hand it's probably not _only_ fat i've lost. I presume that no matter how careful you are you'll always lose at least some other types of tissue along with the fat.
Still it seems like there's definitely a discrepancy somewhere between the theoretical BMR and RMR and activity levels and the estimated calories burnt from specific activities.
On the plus side, in theory that means that when/if i finally reach a weight i like i'll be able to eat a fair bit more than i was expecting. Although that does make me wonder, exactly how much was i eating during the period when i was gaining weight? =P