24 MPG combined immediately makes the 2026 BMW 840i xDrive Convertible an efficient grand tourer, especially considering it’s a luxurious, powerful open-top cruiser with all-wheel drive, designed to transport two adults and their luggage swiftly and stylishly across continents. This isn’t a vehicle bought for outright efficiency, but rather for its blend of performance, comfort, and panache. The 24 MPG is a pleasant bonus, an affirmation that you can indulge in a substantial, opulent convertible without constantly worrying about the fuel gauge. It reassures the driver that long journeys are not only supremely comfortable but also relatively economical for this class of machine. This is a car for the individual who appreciates engineering prowess and a low-stress ownership experience, someone who values subtle nods of approval rather than overt shouts for attention. They choose the 840i Convertible for its grace and the muted thrum of its inline-six, not for drag strip heroics or SUV-like practicality. It’s a statement of taste, and its sensible fuel consumption simply adds to that understated elegance.

City and highway performance

The EPA rates the 840i xDrive Convertible at 21 MPG in the city and 29 MPG on the highway. These figures are highly credible for a vehicle of this caliber. The 21 MPG in city driving reflects the engineering of BMW’s B58 3.0L inline-six, renowned for its smoothness and efficiency, even when navigating stop-and-go traffic. The smooth integration of the standard 8-speed automatic transmission (S8) plays a crucial role here, executing imperceptible shifts that capitalize on the engine’s broad torque band from low RPMs. This allows the vehicle to accelerate with minimal fuss, reducing the need for aggressive throttle inputs that typically consume more fuel. Stop-start technology, while sometimes controversial, contributes noticeably to this city rating by shutting off the engine at idle. On the open road, the 29 MPG highway figure is particularly impressive. The long gearing of the 8-speed transmission, coupled with the engine’s inherent efficiency at cruising speeds, makes the 840i Convertible a true long-distance cruiser. At typical highway speeds, the engine is barely ticking over, operating well within its most efficient range. The xDrive all-wheel-drive system, often perceived as a fuel economy detriment, is managed intelligently, only sending power to the front wheels when traction demands it, otherwise maintaining a rear-biased setup to reduce drivetrain losses. For a vehicle with substantial curb weight and the aerodynamic challenges inherent to a convertible, these highway numbers are genuinely excellent, enabling extended trips between fuel stops and enhancing the grand touring experience.

Annual fuel cost

The EPA estimates an annual fuel cost of $2,400 for the 2026 BMW 840i xDrive Convertible. This figure is based on driving 15,000 miles per year, with a distribution of 45% highway and 55% city driving, and assumes national average fuel prices, typically using premium unleaded gasoline for vehicles like the 840i. For the typical buyer of an 8 Series Convertible, this $2,400 figure is hardly a deterrent. It represents a manageable expense within the broader context of owning a luxury vehicle that starts well into the six-figure range. The engineering efficiency of the B58 engine makes this possible. The individual who purchases this car is not primarily concerned with minimizing every last penny spent on fuel; their motivation is the driving experience, the luxury, and the prestige. However, they appreciate that their indulgence doesn’t come with an exorbitant recurring fuel bill. A $2,400 annual fuel cost means fewer interruptions during long road trips and a lower overall total cost of ownership compared to many less efficient, similarly positioned luxury vehicles. It reinforces the idea that the 840i Convertible offers a blend of performance and practicality without undue financial burden on its operational expenses.

Real-world expectations

In real-world driving, owners of the 2026 BMW 840i xDrive Convertible can generally expect to meet or even slightly exceed the EPA’s combined 24 MPG rating, depending on their driving style and conditions. The inline-six engine and 8-speed automatic are particularly forgiving. Those who primarily cruise on highways, using the adaptive cruise control and smooth power delivery, will likely hover around the 29 MPG mark, possibly even touching 30 MPG on flatter terrain with a light foot. Even in mixed driving, especially if it leans more towards suburban arterial roads rather than congested downtown grids, hitting the 24 MPG combined is entirely achievable. Aggressive driving, with frequent hard acceleration and braking, will naturally cause the numbers to drop, pushing closer to the 21 MPG city rating. However, the character of the 840i Convertible doesn’t inherently encourage such driving. It’s a refined performer, encouraging a smooth, flowing driving style that intrinsically benefits fuel efficiency. The adaptive suspension and effortless power delivery create an environment where frantic driving feels out of place. The most significant variable remains the driver’s lead foot. Someone consistently exploiting the engine’s 335 horsepower will see lower numbers, but even then, the inherent efficiency of the B58 engine and the transmission means the drop isn’t as dramatic as it might be in less refined powertrains. For most owners, the real-world fuel economy will be a pleasant surprise, confirming the EPA figures are an honest representation.

How it compares

The 2026 BMW 840i xDrive Convertible has strong fuel efficiency against its direct competitors. Consider the Porsche 911 Carrera Cabriolet (entry-level): its 3.0L twin-turbo flat-six delivers 20 MPG combined (18 city/25 highway), a notable drop from the BMW’s figures. The Mercedes-Benz CLE 300 Cabriolet, while a size class smaller, offers 25 MPG combined (24 city/33 highway) from its M254 2.0L turbo-four engine but with significantly less power and presence. A more direct competitor in spirit and size might be the Lexus LC 500 Convertible, which, with its naturally aspirated 5.0L V8, manages a meager 18 MPG combined (15 city/25 highway). Even within BMW’s own lineup, the M850i xDrive Convertible, with its more potent 4.4L TwinPower Turbo V8, drops to 19 MPG combined (17 city/24 highway), highlighting the inherent efficiency advantage of the 840i’s inline-six. This comparison clarifies why the 840i appeals to its specific demographic. Buyers of the 840i Convertible are seeking the luxury, prestige, and grand touring capabilities that often come with a V8, but without the associated cost, weight, and, crucially, fuel consumption penalties. They desire a powerful open-top experience, not ultimate track prowess, and the 840i’s fuel economy credentials allow them to enjoy that indulgence with a clear conscience, making cross-country trips more frequent and less costly than its direct rivals. For all BMW fuel economy data, and specifically 840i MPG across all years, our database has detailed information.

Tips to maximize efficiency

Maintain smooth, consistent throttle inputs. The 840i’s B58 engine delivers abundant torque from low RPMs, so there’s rarely a need to aggressively stomp on the accelerator. Gentle acceleration and deceleration optimize the engine’s operation and prevent unnecessary fuel consumption.

Use the Driving Experience Control modes. Switching to “ECO PRO” mode will adjust throttle response, transmission shift points, and even climate control settings to prioritize fuel efficiency, making a noticeable difference in daily driving. While “Sport” modes are tempting, they inherently consume more fuel.

Regularly check tire pressure. Underinflated tires increase rolling resistance, forcing the engine to work harder. Keeping the tires at the manufacturer’s recommended pressure is one of the simplest and most effective ways to maintain optimal fuel economy.

Plan your journeys and combine errands. Minimizing cold starts and short trips, especially in urban environments, helps because the engine operates less efficiently when cold. A warm engine is a more efficient engine.

Employ the coasting function when safe and appropriate. In some drive modes, the 8-speed automatic transmission will decouple the engine when you lift off the accelerator, allowing the car to glide under its own momentum, effectively saving fuel during descents or when approaching a stop.