IFR Fuel Planning Calculator

FAR 91.167 sets the legal minimum fuel for IFR flight: enough to reach the first airport of intended landing, then to the alternate (if one is required), then fly for 45 more minutes at normal cruising speed. This calculator builds that requirement up piece by piece. Enroute fuel comes from dividing destination distance by your expected groundspeed to get flight time, then multiplying by your cruise fuel burn rate; the same logic runs a second time for the alternate leg, using its own distance and groundspeed since diversion speed often differs from the primary cruise leg. Reserve fuel converts your reserve minutes (45 by regulation, though you can enter more) into gallons at the same burn rate, and a flat taxi-fuel allowance covers ground operations that never show up in enroute burn figures.

Those four pieces sum to a subtotal, to which a contingency percentage is applied — a personal safety margin for wind, routing changes, or holding that the regulation itself doesn't mandate but prudent planning usually adds. The total required fuel is then compared against your tank's usable capacity to show a fuel margin (negative means you're planning to depart illegal or unsafe), alongside the aircraft's maximum still-air endurance at that burn rate and an estimated dollar cost. Remember this only reflects gallons and minutes at your assumed burn rate and groundspeed — real winds, altitude changes, and engine leaning will move the actual numbers, so build in enough contingency that a forecast miss doesn't erase your legal reserve.