Calculating the juice on futures is pretty easy. We start by converting all the odds to one scale. For example, a book may list a team as 5 to 2 so we show it as 2.5 to 1. Next calculate percentages as 1/(Odds+1).
Examples:
1 to 1 = 1/(1+1) = 50%
2 to 1 = 1/(2+1) =33.33%
3 to 1 = 1/(3+1) = 25%
Finally add up all the percentages. The more it goes over 100%, the more juice the book gets.

Here are the futures for AFC teams to win the AFC Championship.
From Bet365 and Excel:
IND Colts , Bet365 Odds: 2.87 , Calc: 0.258397933
NE Patriots , Bet365 Odds: 4.5 , Calc: 0.181818182
PIT Steelers , Bet365 Odds: 7 , Calc: 0.125
CIN Bengals , Bet365 Odds: 9 , Calc: 0.1
SD Chargers , Bet365 Odds: 13 , Calc: 0.071428571
JAX Jaguars , Bet365 Odds: 15 , Calc: 0.0625
DEN Broncos , Bet365 Odds: 15 , Calc: 0.0625
KC Chiefs , Bet365 Odds: 17 , Calc: 0.055555556
BAL Ravens , Bet365 Odds: 19 , Calc: 0.05
MIA Dolphins , Bet365 Odds: 19 , Calc: 0.05
BUF Bills , Bet365 Odds: 41 , Calc: 0.023809524
NY Jets , Bet365 Odds: 51 , Calc: 0.019230769
OAK Raiders , Bet365 Odds: 51 , Calc: 0.019230769
HOU Texans , Bet365 Odds: 101 , Calc: 0.009803922
CLE Browns , Bet365 Odds: 101 , Calc: 0.009803922
TEN Titans , Bet365 Odds: 126 , Calc: 0.007874016
TOTAL 1.106953163
As you can see at the time of this writing the total is just over 110%