24 MPG combined is the fuel economy for open-air motoring in the 2025 BMW 840i Convertible. It’s a blend of performance and relative efficiency, acceptable to a buyer who prioritizes the experience of wind in their hair and the sound of a BMW inline-six.

City and highway performance

That 24 combined miles per gallon breaks down to 21 MPG in the city and 29 MPG on the highway. The urban rating reflects stop-and-go traffic, where the 840i’s eight-speed automatic transmission manages the engine’s power. The highway number is more respectable. Cruising at steady speeds allows the engine to relax, taking advantage of its efficiency and the tall gearing of the transmission to deliver nearly 30 MPG. This is reassuring for longer journeys, suggesting that while the 840i Convertible is built for weekend getaways, fuel costs won’t prohibit extended road trips.

Annual fuel cost

The EPA estimates the annual fuel cost for the 2025 BMW 840i Convertible at $2,400. This figure is based on driving 15,000 miles per year, with a mix of city and highway driving, using the national average fuel price. Owners should consider this a baseline, as individual driving habits and local fuel prices will influence the actual cost. Someone driving predominantly in congested urban environments, or who enjoys exploring the engine’s performance, will likely exceed this annual figure. Premium fuel is required, contributing to the overall expense.

Real-world expectations

While the EPA provides a standardized benchmark, real-world fuel economy often varies. Drivers who prioritize acceleration and regularly engage the sport driving modes can expect lower numbers than the EPA estimates. Conversely, those who adopt a more relaxed driving style and make greater use of the car’s adaptive cruise control on the highway might see slightly better figures. Wind conditions, tire pressures, and even the use of accessories like air conditioning can influence fuel consumption. The 840i convertible’s extra weight due to its reinforced chassis and folding top mechanism comes at a cost compared to the coupe variant. Explore 840I MPG across all years to see historical trends.

How it compares

In the realm of luxury convertibles, the 840i’s fuel economy lands in the middle of the pack. The Mercedes-Benz SL 55 AMG, a more powerful and performance-oriented car, achieves a combined 16 MPG. A Porsche 911 Carrera Cabriolet, with a similar engine configuration, manages roughly 20 MPG combined, offering slightly better efficiency, but sacrifices some of the 840i’s grand-touring comfort. The Lexus LC 500 Convertible, equipped with a V8, gets around 18 MPG combined. Potential buyers cross-shopping these models understand that performance and luxury come at a price, with fuel economy being one of the trade-offs. See all Bmw fuel economy data for brand comparisons.

Tips to maximize efficiency

Use the 840i’s “Comfort” driving mode for everyday commutes. This setting optimizes the engine and transmission for efficiency, softening throttle response and encouraging earlier upshifts.

Ensure that your tires are properly inflated. Correct tire pressure reduces rolling resistance, improving fuel economy. Check the sticker on the driver’s side doorjamb for the recommended pressure.

Anticipate traffic flow to minimize unnecessary braking and acceleration. Smooth driving reduces fuel consumption by maintaining momentum and preventing abrupt changes in speed.

Avoid carrying excess weight in the car, as this increases the engine’s workload. Remove any unnecessary items from the trunk to improve fuel efficiency. Even small weight reductions can make a difference over time.

On longer trips, use the adaptive cruise control to maintain a consistent speed and distance from other vehicles. This system can help optimize fuel economy, particularly on relatively flat stretches of highway.