I calculated mine this way. Took, previous week's fuel cost, multiplied it times 4 to get an approximate monthly, fuel cost, as I've added 6-7 new aircraft in the last 2 weeks. Then from that monthly estimate divide by 2 to get the fuel at your home base. Finally multiply that by what ever the fuel contract's savings are. Then compare it to the contracts price.
here's my example,
837,000*4= $3,348,000 total monthly fuel cost based off of prior week's income statement
3,348,000/2= $1,674,000 approximate fuel from my base
1,674,000*.05 = $83,700 < $152,500 savings is less than contract price, so it is not worth it.
Hope this example helps clarify.