CASM excluding fuel

An airline industry metric measuring the cost to fly one seat-mile, excluding the highly volatile cost of aircraft fuel.

Cost per Available Seat Mile (CASM) excluding fuel, often abbreviated as CASM-ex, is a key efficiency metric used to evaluate an airline's underlying operational cost structure. By stripping out aircraft fuel expenses, which fluctuate wildly based on global commodity markets and geopolitical events, investors can isolate and analyze the expenses that airline management can directly control. These controllable costs include labor, aircraft maintenance, airport rent, marketing, and administrative overhead. To calculate CASM-ex, an airline's total fuel expense is subtracted from its total operating expenses, and the resulting non-fuel cost is divided by the total Available Seat Miles (ASMs) flown during the same period. ASMs represent the total passenger capacity of the airline, calculated by multiplying the number of available seats on an aircraft by the distance of the flights. For investors, tracking CASM-ex is critical to understanding whether an airline is managing its internal cost structure effectively. A rising CASM-ex indicates that the airline's operations are becoming less efficient, which can severely compress profit margins if ticket prices (unit revenues) do not rise fast enough to offset the inflation. Conversely, a flat or declining CASM-ex demonstrates strong cost discipline and operational leverage. When analyzing this metric, investors look for CASM-ex growth to remain below general inflation or, ideally, below the rate of unit revenue growth. A common pitfall is comparing CASM-ex across airlines with vastly different business models; for instance, ultra-low-cost carriers naturally have much lower baseline CASM-ex than premium legacy carriers due to different service levels and stage lengths.

An airline reports total operating expenses of $5,000,000,000, of which $1,500,000,000 was spent on aircraft fuel. During the same quarter, the airline operated 35,000,000,000 available seat miles (ASMs). Its CASM excluding fuel is calculated as: ($5,000,000,000 - $1,500,000,000) / 35,000,000,000 = $0.10, or 10 cents per seat-mile.