24 MPG combined might, at first glance, seem like a mere footnote for a vehicle with the undeniable presence and aspirations of the 2026 BMW 840i Convertible. Yet, for an open-top, two-door luxury grand tourer powered by a smooth inline-six, that figure represents a commendable balance between its effortlessly potent performance and the kind of efficiency buyers now expect, even in this rarefied segment. This isn’t a car purchased for its frugality; it’s acquired for its sun-drenched cruising, its ability to devour highway miles in opulent comfort, and the precise, engaging dynamics BMW is renowned for. The fuel economy, therefore, is an agreeable bonus, a sign that the luxurious indulgence doesn’t come with an entirely unreasonable thirst.

City and highway performance

The 840i Convertible’s 21 MPG in the city reflects the inherent challenges of moving a substantial, well-appointed machine through stop-and-go traffic. While the 3.0L B58 turbocharged inline-six is remarkably refined and flexible, its 375 horsepower and 398 lb-ft of torque are always on tap, and the smooth ZF 8-speed automatic transmission is geared to deliver that power with authority, not necessarily maximum parsimony, in urban environments. However, the true strength of this powertrain, and where its efficiency truly shines, is on the open road. At 29 MPG highway, the 840i Convertible proves itself an exceptional long-distance companion. This isn’t merely an arbitrary figure; it directly speaks to the car’s grand touring mission. Sustained cruising at highway speeds allows the engine to operate within its most efficient RPM range, the aerodynamic profile of the car to minimize drag, and the advanced drivetrain to deliver those effortless miles with remarkable grace and minimal fuel consumption for its class. This efficiency allows for longer stretches between fuel stops, enhancing the carefree, continent-crossing experience that defines the 8 Series Convertible.

Annual fuel cost

The EPA estimates an annual fuel cost of $2,400 for the 2026 BMW 840i Convertible. This figure is calculated based on an average of 15,000 miles driven per year, split between city and highway driving, and using national average fuel prices for premium gasoline. For the typical 8 Series Convertible owner, this annual cost is comfortably within their budget and represents a negligible fraction of the vehicle’s overall cost of ownership, which includes depreciation, insurance, and maintenance. Buyers in this segment are not deterred by a few thousand dollars in annual fuel expenditure; their priority is the uncompromising luxury, performance, and emotional connection this vehicle provides. The $2,400 figure serves as a straightforward benchmark, reassuring buyers that their indulgence isn’t accompanied by an unforeseen and burdensome running cost.

Real-world expectations

In real-world driving conditions, the 2026 BMW 840i Convertible’s fuel economy will largely align with the EPA estimates for most conscientious drivers. However, the powerful B58 engine, with its immediate torque delivery and intoxicating exhaust note, can easily tempt drivers into more spirited acceleration. Frequent excursions into the higher RPMs, particularly when engaging Sport or Sport+ driving modes, will naturally see fuel consumption increase. Likewise, sustained top-down cruising at higher speeds on the highway, while exhilarating, introduces additional aerodynamic drag, slightly impacting the upper end of the highway MPG. Conversely, drivers who prioritize smooth, relaxed cruising, using the adaptive cruise control and anticipating traffic, will often find themselves matching or even exceeding the EPA figures. The key takeaway is that the vehicle’s character strongly invites dynamic driving, and those moments of automotive joy inherently consume more fuel. But for its primary use, effortless long-distance travel and stylish urban journeys, it delivers as promised.

How it compares

The 840i Convertible occupies a unique space, blending sporty aesthetics with genuine luxury and grand touring capability. Its 840i MPG across all years holds up well against direct and indirect competitors. Consider the Porsche 911 Carrera Cabriolet, a more overtly performance-focused machine. A 2026 911 Carrera Cabriolet with its 3.0L twin-turbo flat-six typically achieves around 21 MPG combined (18 city/25 highway), a noticeably lower figure than the BMW, reflecting its more aggressive tuning and weight. On the other hand, a Mercedes-Benz SL 450 Roadster, often seen as a direct rival, uses a similar 3.0L inline-six and achieves an estimated 23 MPG combined (20 city/27 highway), placing it remarkably close to the BMW, but often with a slightly different driving character. Stepping into more luxury-focused territory, a Lexus LC 500 Convertible, powered by a naturally aspirated 5.0L V8, manages a significantly lower 18 MPG combined (16 city/25 highway). These comparisons highlight that the 840i Convertible strikes an impressive balance, offering strong performance and luxurious comfort without falling far behind, or even leading, its peers in the efficiency stakes. This isn’t about bragging rights at the pump; it’s about not being penalized for choosing an advanced open-top tourer.

Tips to maximize efficiency

While the 840i Convertible isn’t about extreme frugality, some practices can ensure you consistently achieve the upper end of its efficiency ratings. Smooth, deliberate acceleration and braking are important; the engine’s ample torque means there’s rarely a need to aggressively stomp on the throttle, even in city driving. Anticipatory driving, looking ahead for traffic lights and flow, reduces the need for heavy braking and subsequent re-acceleration, which are big fuel consumers. Use the car’s Eco Pro driving mode, especially in less urgent driving scenarios. This mode subtly adjusts throttle response, transmission shift points, and climate control to prioritize efficiency without significantly detracting from the driving experience. Finally, maintaining correct tire pressures is always essential; under-inflated tires increase rolling resistance, forcing the engine to work harder. Keeping up with recommended service intervals, ensuring the engine and drivetrain are operating optimally, will also contribute to consistent fuel economy throughout the vehicle’s lifespan, ensuring your driving enjoyment is maximized, whether you’re navigating urban streets or cruising the scenic routes, often with the top down. For more detailed information on maximizing fuel economy across the brand’s diverse portfolio, explore all Bmw fuel economy data.