The thing is, a program like Fitday - or any other for that matter - can not account for the concurrent boost in metabolism from a high intensity session, let alone the fact that everyone burns calories at different rates.
There are a set of equations (i am not about to look them up for this purpose) for such things, but they are 'general guidelines'. The metabolism is still not 100% understood and as such is impossible to account for all variables.
I have used Fitday and it is a useful tool, but i would never take anything like that at its word. It is useful for a ball-park figure - not as an accurate tool to calculate expenditure and intake of energy.
If you are the most stringent with the data you input (not to Fitday per se - as i don't know what equations they use - but calculated everything fully from scratch, i would say the range would be better than 'ball-park'.. but not 100% still).
When you take into account the LBM, weight, age, sex and height of a person - you get a moderately accurate snapshot of their metabolism - this is NOT totally accurate and two men with the same stat's as above will still have differences in their metabolisms.. but as i said 'ball-park'.
Then add (or subtract) the general activities one partakes in (stair climbing, walking, sitting, eating, etc) and add the exercise activities one does.. such as football for 90mins or weights for 60mins. These again are ball park expenditures.. as for example 90mins of 75% 1RM load with controlled to the dot intensity, will burn different amounts of calories in different people, and it will raise the metabolism for a period thereafter too.. which will also differ greatly - dependant on hundreds of factors.
All this goes into BMR and caloric requirements - and it is common for GOOD PT's to do this sort of thing for the clients that require it.
It is better than not knowing - so Fitday is good. But it is not 100%, no.
Is that you in your profile? I always thought it was but suddenly i wonder - i will be disappointed if it isnt