Recipe calculators showing vastly different results

[Sea_of_Shells]

I understand that recipe calculators aren't 100%, but the three that I've used have given me bewildering results.

The first one was:
http://powersbrewery.home.comcast.net/~powersbrewery/mastercalculator.html
Predicted OG: 1.063
Final Gravity: 1.016
IBUs: 53
ABV:6.4

The second one was:
http://byo.com/resources/brewing
Predicted OG: 1.054
Final Gravity: 1.014
IBUs: 47
ABV:5.2


The third one was:
http://www.brewersfriend.com/homebrew/recipe/calculator
Predicted OG: 1.075
Final Gravity: 1.019
IBUs: 25
ABV:7.3

The recipe in question is an extract recipe with steeping grains which I'm hoping will produce a hoppy porter/black IPA. If you want me to post the recipe, I will.

Why the vast difference here? The ingrediants that I selected were all identical on each site. Is there one that is more accurate that the other?

 

[duboman]

Sometimes it comes down to the default values for potential extract and the AA value assigned to the hops that are used by the software.

 

[MuddyCreek]

I blame society.

 

[beergolf]

A lot depends on the default settings. The attenuation sttings are probably different. Also the bitterness will vary a lot using different scales. I use Tinseth. I find that Rager or the other are not as consistent for me. Whichever you choose , just get used to it. and then you can ompare brew to brew,