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  • Specs840i · 718

BMW 840i G15 vs Porsche 718 Cayman: which is cheaper to run?

What each kilometre costs, depending on your driving profile and how you charge. Annual projection and cumulative savings over 10 years.

limousine · 2020 vs 2018 · 15,000 km/an · Mixed · Petrol 95 2.17 €/L · Methodology
Annual mileage
15,000 km
5,000 km50,000 km
Driving mix

30 % City · 50 % Road · 20 % Motorway

Fuel price
Petrol 95 2.17 €/L · Diesel 2.38 €/Lprix-carburants.gouv.fr — moyenne nationale du 05/10/2026 ; EDF Tarif Bleu Base au 01/08/2026 ; DC autoroute : moyenne des réseaux sans abonnement

Result · yearly energy cost

ABMW 840i G15

2,477 €per year

7,6 L/100 km weighted · 16.51 € per 100 km · 1 141 L per year

Gap759 € per yearin favour of the 840i (−23 %)≈ 350 L petrol 95
BPorsche 718 Cayman

3,236 €per year

9,9 L/100 km weighted · 21.57 € per 100 km · 1 491 L per year

The verdict changes with your usage
ProfileSplitAA · 840iBB · 718Gap
City70 / 25 / 570 % city · 25 % road · 5 % motorway2,747 €3,486 €739 € · 840i
Mixed30 / 50 / 2030 % city · 50 % road · 20 % motorway2,477 €3,236 €759 € · 840i
Long-distance10 / 40 / 5010 % city · 40 % road · 50 % motorway2,269 €3,008 €739 € · 840i

Cumulative saving for the 840i

1 year
759 €
3 years
2,276 €
5 years
3,793 €
10 years
7,585 €

Energy only. Excludes purchase, insurance, servicing, depreciation.

What produces these figures

WLTP combined
7.3 L/100 km · 9.8 L/100 km
Powertrain
Combustion · Combustion
Power
340 ch · 300 ch
Kerb weight
1,710 kg · 1,335 kg

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Frequently asked questions

On a 100 km mixed trip, the BMW 840i is about 25% cheaper than the Porsche 718 Cayman with default parameters. This ratio shifts with your actual energy prices - simulate for your profile.

The BMW 840i is cheaper across all distances with default rates. If your energy prices differ significantly, simulate to see the real impact on your budget.