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718vs420iPetrol
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  • Specs718 · 420i

Porsche 718 Cayman vs BMW 420i F32: 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.

sports car · 2018 vs 2020 · 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

APorsche 718 Cayman

3,236 €per year

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

Gap1,263 € per yearin favour of the 420i (−39 %)≈ 582 L petrol 95
BBMW 420i F32

1,973 €per year

6,1 L/100 km weighted · 13.15 € per 100 km · 909 L per year

The verdict changes with your usage
ProfileSplitAA · 718BB · 420iGap
City70 / 25 / 570 % city · 25 % road · 5 % motorway3,486 €2,194 €1,292 € · 420i
Mixed30 / 50 / 2030 % city · 50 % road · 20 % motorway3,236 €1,973 €1,263 € · 420i
Long-distance10 / 40 / 5010 % city · 40 % road · 50 % motorway3,008 €1,803 €1,204 € · 420i

Cumulative saving for the 420i

1 year
1,263 €
3 years
3,789 €
5 years
6,315 €
10 years
12,630 €

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

What produces these figures

WLTP combined
9.8 L/100 km · 5.8 L/100 km
Powertrain
Combustion · Combustion
Power
300 ch · 184 ch
Kerb weight
1,335 kg · 1,525 kg

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Frequently asked questions

On a 100 km mixed trip, the BMW 420i is about 40% cheaper than the Porsche 718 Cayman with default parameters. This ratio shifts with your actual energy prices - simulate for your profile.

The BMW 420i is cheaper across all distances with default rates. If your energy prices differ significantly, simulate to see the real impact on your budget.