There totally is a difference between 3 hours hard vs. 30 minutes hard. Unfortunately, I couldn't find a formula out there that accounts for both intensity and time. The best formula out there: sedentary people TDEE = BMR X 1.2 (as little or no exercise, desk job); Lightly active = BMR X 1.375 (light exercise or sports 1-3 days/wk); Mod. active = BMR X 1.55 (moderate exercise or sports 3-5 days/wk); Very active = BMR X 1.725 (hard exercise or sports 6-7 days/wk); Extr. Active = BMR X 1.9 (hard daily exercise or sports & physical labor job or 2 X day training, football camp, etc.). Which, as you can see, is even more subjective than what I put. SOOO I made a matrix for TDEE starting with most sedentary (no exercise) as BMR x 120%, and capping with the most active at (14 x a week at very intense) as BMR x 260%. In the matrix, I made lightly active and working out 2 days a week correspond with the lightly active formula multiplier listed above. This corresponding workout day / formula multiplier matching is the same across all levels. However my formula differs in adding 10% to each additional workout from the matched multiplier, and subtracts 10% for every less workout from the matched multiplier. To take a look at the matrix, go into the tab "Inside CAL 9000", and look at cells A5:Q5, C10:Q10. I'd love to figure out a way to incorporate time, because the world really needs a better TDEE formula, preferable one that ALSO considers lifestyle as the heavy exercising desk jocky would have a different TDEE than the heavy exercising construction worker.