31 MPG combined isn’t going to set any hypermiling records, but for the 2021 BMW i3 with its quirky range extender, it represents a very specific type of freedom. This isn’t about saving money on gas in the traditional sense; it’s about alleviating range anxiety for buyers who love the i3’s electric drivetrain and urban-friendly dimensions, but need a safety net for longer trips. The i3 REx is a specialized tool for a particular job.

City and highway performance

The EPA estimates the 2021 BMW i3 REx at 30 MPG in the city and 31 MPG on the highway. These numbers are remarkably consistent, highlighting the range extender’s role as a supplement to the electric motor, rather than a primary power source. The 0.6L two-cylinder engine primarily exists to maintain the battery’s charge level, allowing drivers to continue their journeys when the all-electric range is depleted. Because of this, it’s not taxed as much in stop-and-go driving as a conventional gasoline engine. This explains the very similar city and highway MPG ratings. See I3 MPG across all years.

Annual fuel cost

The EPA estimates the annual fuel cost for the 2021 BMW i3 with Range Extender at exactly $1,850. This figure is based on driving 15,000 miles per year, using a combination of city and highway roads, and assumes the national average fuel price. Given the i3’s electric nature and reliance on electric charging, this figure represents the worst case if you were to drive it almost exclusively on gasoline. Most i3 REx owners will likely spend far less than $1,850 annually, because they usually charge the electric powertrain. The range extender is truly a “just in case” addition.

Real-world expectations

While the EPA numbers offer a baseline, real-world fuel economy depends heavily on driving habits and charging availability. An owner who religiously plugs in their i3 and primarily uses the range extender for occasional longer trips may only visit a gas station a handful of times per year. Conversely, someone who neglects charging and relies heavily on the range extender will see significantly lower MPG figures. The i3 REx’s fuel consumption is directly proportional to how much you lean on that tiny two-cylinder. It’s a tool, not a crutch.

How it compares

Comparing the i3 REx to other vehicles requires a nuanced approach. On electric power alone, its efficiency is unmatched, but factoring in its 31 MPG when the range extender kicks in puts it in a different league. The Chevrolet Bolt, for example, offers significantly better all-electric range and zero gasoline consumption for most drivers. The Nissan Leaf, while often less expensive, also operates solely on electricity. Even hybrid vehicles like the Toyota Prius (56 MPG combined) or the Hyundai Ioniq (59 MPG combined) deliver better MPG figures overall. However, those cars lack the i3’s unique mix of electric driving and quirky BMW character. Buyers choose the i3 for its design and personality, and are willing to concede some fuel economy in exchange for those attributes.

Tips to maximize efficiency

Prioritize charging whenever possible. The more miles you cover on electricity, the less the range extender will run, directly reducing fuel consumption. Make plugging in at home or work a routine to keep the battery topped off. This will also greatly reduce your running costs.

Drive smoothly and conservatively. Rapid acceleration and hard braking drain the battery quickly, forcing the range extender to work harder and burn more fuel. As with any electric vehicle, maintaining a steady pace and anticipating traffic conditions will conserve energy.

Keep the tires properly inflated. Underinflated tires increase rolling resistance, requiring more energy to maintain speed. Check your tire pressure regularly and inflate them to the recommended level, found on the doorjamb or in the owner’s manual.

Minimize the use of energy-intensive accessories. Air conditioning and heating can put a significant strain on the battery, especially when driving in extreme temperatures. Pre-condition the cabin while the car is still plugged in to reduce the initial load on the battery once you start driving. See all Bmw fuel economy data.