26 MPG combined is a perfectly acceptable figure for the 2015 BMW 428i Convertible. It won’t win any hypermiling competitions, but that’s hardly the point of a stylish, open-top four-seater designed for weekend getaways and boulevard cruising. This car is about the experience, the feeling of wind in your hair (or what’s left of it), and the badge prestige, not squeezing every last mile from a gallon of premium fuel.

City and highway performance

The EPA estimates peg the 428i Convertible at 23 MPG in the city and 33 MPG on the highway. This spread reflects the car’s character: eager and responsive around town thanks to the turbocharged engine, yet relaxed and efficient enough for longer journeys. That 33 MPG highway figure is particularly useful for those weekend trips to wine country or coastal drives, making the 428i a practical choice despite its focus on style. The smooth-shifting eight-speed automatic transmission (S8) helps by keeping the engine in its sweet spot both for performance and fuel efficiency.

Annual fuel cost

The EPA estimates the annual fuel cost for the 2015 BMW 428i Convertible at $2,250. This figure is based on driving 15,000 miles per year and using the national average fuel price at the time of calculation. Your actual fuel costs will vary depending on your driving habits, the type of fuel you purchase, and where you live. However, $2,250 provides a useful benchmark for budgeting and comparison shopping.

Real-world expectations

While the EPA figures provide a good starting point, real-world fuel economy often differs. Drivers who frequently engage Sport mode, drive aggressively, or spend most of their time in stop-and-go traffic will likely see numbers closer to the city rating. On the other hand, disciplined drivers who stick to steady highway speeds can often exceed the EPA’s 33 MPG estimate. The 428i’s driving dynamics encourage spirited driving, so achieving the EPA combined figure requires some restraint. Premium fuel is recommended, adding to the overall running costs.

How it compares

The 428i Convertible’s fuel economy is competitive within its segment. Consider the Audi A3 Cabriolet, another stylish German convertible. The A3 Cabriolet with its 1.8T engine achieves around 28 MPG combined, slightly better than the 428i. However, the A3 doesn’t offer the same level of performance or interior space. The Mercedes-Benz C-Class Cabriolet, specifically the C300 variant, posts similar numbers to the 428i, hovering around 25 MPG combined. Buyers often cross-shop these three, and the fuel economy differences are rarely a deciding factor. They are more likely to look at styling, brand cachet and driving dynamics. You can explore all Bmw fuel economy data on this site. For those with a specific interest on this model, find even more 428I MPG across all years too.

Tips to maximize efficiency

Smooth and steady acceleration is your best friend. Avoid sudden bursts of speed and try to anticipate traffic flow to minimize braking. The 428i’s turbocharger provides plenty of torque at low RPM, so there’s no need to constantly rev the engine to extract performance.

Tire pressure plays an important role in fuel economy. Check your tires regularly and ensure they are inflated to the recommended pressure. Under-inflated tires increase rolling resistance, which reduces fuel efficiency. The correct tire pressure is usually found on a sticker inside the driver’s side door jamb.

Reduce unnecessary weight. Carrying extra cargo in the trunk adds to the vehicle’s overall weight, forcing the engine to work harder and consume more fuel. Remove any items you don’t need for your daily commutes.

Take advantage of the 428i’s driving modes. Comfort mode prioritizes fuel efficiency over performance, while Eco Pro mode optimizes various vehicle systems to further conserve fuel. These modes can make a noticeable difference on longer journeys.

Consider limiting top-down driving at higher speeds. While it’s tempting to always have the top down, especially on the open road, the added aerodynamic drag significantly reduces fuel efficiency. Raising the top for highway driving can noticeably improve your MPG.