Against 344 other Hybrid cars rated 2024–2026, the M340i beats their 28 mpg average by 1 mpg, about $47 a year. Averaged over the years each was sold, the most economical engine since 2020, the 3L 4-cyl Hybrid (2025), does 29 mpg and the thirstiest, the 3L 6-cyl (2020), 25: $212 a year apart.
Every BMW M340i engine, compared
Yearly cost assumes 12,000 miles at $3.20 a gallon.
| Engine | Combined | City / Highway | Years | Fuel per year |
|---|---|---|---|---|
| 3L 4-cyl Hybrid | 27 / 33 | 2025–2025 | $1,324 | |
| 3L 6-cyl Hybrid | 23.8 / 31.8 | 2021–2026 | $1,444 | |
| 3L 6-cyl | 22 / 30 | 2020–2020 | $1,536 |
What that actually costs
Against its rivals in the same model years, the Cadillac CT4 gets 22.5 mpg, next to 29 mpg for the 2026 M340i. The M340i is the cheapest of them to run: $383 a year less than the Cadillac CT4.
| Measure | Value |
|---|---|
| Cost per mile (2026) | $0.110 |
| Fuel per year | $1,324 |
| Fuel over five years | $6,620 |
| Against other Hybrid cars, 2024–2026 | −$47 a year |
| EPA's own estimate | $2,886 a year |
City or highway — who is this car for
The 2026 BMW M340i gives up 6 mpg in town: 33 on the highway against 27 in the city, $258 a year if every mile were city driving.
| Measure | Value | Reading |
|---|---|---|
| City (2026) | 27 mpg | $1,422 a year if you only drive in town |
| Highway | 33 mpg | $1,164 a year if you mostly commute |
| Gap | +6 mpg (22%) | Typical for its type |
How the M340i changed over the years
The M340i peaked in 2026 at 29 mpg (27 city, 33 highway) and was at its thirstiest in 2020 at 25 — 4 mpg apart, or $212 a year in fuel between buying one year and the other. The biggest single-year change came in 2025: 26 to 29 mpg.
| Model year | Combined | City / Highway | Engines offered | Fuel per year |
|---|---|---|---|---|
| 2026 | 27 / 33 | 1 | $1,324 | |
| 2025 | 27 / 33 | 1 | $1,324 | |
| 2024 | 23 / 31 | 1 | $1,477 | |
| 2023 | 23 / 31 | 1 | $1,477 | |
| 2022 | 23 / 32 | 1 | $1,477 | |
| 2021 | 23 / 32 | 1 | $1,477 | |
| 2020 | 22 / 30 | 1 | $1,536 |
MPG is a number. Dollars per year is the answer.
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How we count
This page rests on 7 EPA ratings of the BMW M340i — 3 engines across 2020–2026. The mileage is EPA's laboratory figure, unchanged; the yearly bill is ours, at 12,000 miles and $3.20 a gallon, against EPA's own estimate of $2,886. Full method.
Frequently asked questions
What mpg does the 2026 BMW M340i get?
29 mpg combined, 27 city and 33 highway, per EPA. Across every year since 2020 the M340i has averaged 26.7 mpg.
Is the 2026 M340i more efficient than the 2025?
About the same: 29 against 29 mpg combined.
Which M340i year has the best gas mileage?
The 2026, at 29 mpg combined (27 city, 33 highway), which is also the latest model year we hold.
Does the M340i get better gas mileage than the Cadillac CT4?
Yes: 29 mpg for the 2026 M340i against 22.5 for the 2026 Cadillac CT4, about $383 a year less to run.
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