Different calculators, different results...which to use?

JO4IT

I'm confused about the number of calories that I should be eating. I did read a lot of the "newbie posts" and am grasping a bit about the whole issue with exercise and the concept of "eating back the calories"

What I don't understand is why there is such a difference in calories required calculations from the MFP site and the Fat2Fit site. I really want to get that correct. I used to do Weight Watchers and so I know that it isn't good to eat too little either. I'm especially worried about the number for my dh a because I am encouraging him to join me in keeping track.

For the two calculators I used "no exercise" for MFP and Sedentary for the F2F, so that I could more easily compare. That's pretty accurate for how we are now, both have desk jobs, full-time. I plan on starting to exercise and will then eat back those calorie.

Here's our numbers:
Me
Age:48
Height: 5'6
CW: 168
GW: 135
MFP says only 1200 calories a day
Fat2Fit calculators say 1592 a day

For DH even bigger of a difference
Age 48
Height: 6' 1
CW: 252
GW: 205
MFP says only 1580 cals per day
Fat2Fit calculators say 2296

Why is there such a difference between the two calculators? I just don't want to get my dh started keeping track of his calorie intake and then have him cranky and hungry, when really his target calorie intake should be much higher! (oh, and I don't want to be cranky either!)

Any insight would be most helpful.

Thanks,
Jo