Can Someone Help with my Maths Please?

Hi All,
 
Ok, I give up - I suck at maths. I can't understand how this can be so hard, but for whatever reason, this just isn't stacking up. I'm trying to accurately calculate my maintenance calorie level based on a spreadsheet I keep which details daily calorie intake and daily exercise burn.
 
I'm pretty sure my calorie intake calculations are accurate to about 5%, and most of my exercise is done with a heart rate monitor so I'm confident the calorie burn is pretty accurate as well. So in my simple mind, weekly intake minus weekly calorie burn is my overall "calorie base", from which I need to add or subtract the weekly weight gain or loss.
 
So, Week 1:
 
Intake: 16187 cals
Exercise: 2492 cals
Result: Lost 5600 cals
 
Week 2:
 
Intake: 21267 cals
Exercise: 2492 cals
Result: Gained 5600 cals
 
So the base totals (intake minus exercise) of these two weeks are about 5100 cals apart, so at first glance I thought that was quite promising. But then I realised the difference between week 1 and week 2 is actually 11,200 cals, since one week was a gain, the other a loss. So either I'm miscounting calorie intake by about 1.5lbs a week(!) or my maths is wrong somewhere.
 
I hope it's the maths - can anyone help me out with this?
 
Many thanks.

This is quite an inaccurate method as you are assuming that all weight lost/gained is fat mass when water levels fluctuate greatly in most people.
 
A better method would be to stick to a fixed calorie intake and exercise regime and track the change in your weight over several weeks.

Can't believe no one has come up with the obvious post to this thread title lol

1+1=2, 2+2=4

😉

Thanks CC, yes that is the plan but I'm attempting to find a decent starting point to begin at. I'm actually trying to gain muscle mass rather than lose weight, so I guess I'll just err on the higher calories side and see how we go.

Where are you getting the gain and loss values from?!?

It's a set of digital scales - it did cross my mind they might be wrong, but they seem to give me the same reading two days running generally (I weight once a week and then the following day if I'm a bit unsure).

it is impossible to calculate fat loss as simply as that. there are many other factors at play mainly water and glycogen. keep at a moderate deficit for a few weeks and tweek as necessary. it is believed that a pound of fat is 3500 cals but a 3500 cal deficit will not work out like that.