Fuel weight calculation (I know one person who printed up a few of these, and kept them in the nav bag for those occasions when they were necessary)
MLW (Max Landing Weight):__________
+ Trip Fuel:__________
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= Trip Limit:__________
MTOW (Max Take Off Weight) =__________
[Cross out the higher figure]
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- EZFW (Estimated Zero Fuel Weight):__________
= MFL (Max Fuel Load):__________
You get the estimated zero fuel weight from the flight plan, of course (assuming it's prepared for you). Round DOWN the trip fuel (and even take off a bit), to allow for short cuts en-route (burn less, and you arrive with too much weight to land!). Round UP the EZFW (if a few more passengers turn up, you might be too heavy to take off!)