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718vs420iPetrol
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  • PerformancePerformance0-100, top speed
  • ConsumptionConsumptionYearly cost
  • Specs718 · 420i

Porsche 718 Boxster S vs BMW 420i Convertible G22: 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 2021 · 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 Boxster S

4,283 €per year

13,2 L/100 km weighted · 28.56 € per 100 km · 1 974 L per year

Gap2,216 € per yearin favour of the 420i Convertible (−52 %)≈ 1,021 L petrol 95
BBMW 420i Convertible G22

2,067 €per year

6,3 L/100 km weighted · 13.78 € per 100 km · 953 L per year

The verdict changes with your usage
ProfileSplitAA · 718BB · 420iGap
City70 / 25 / 570 % city · 25 % road · 5 % motorway5,575 €2,270 €3,305 € · 420i
Mixed30 / 50 / 2030 % city · 50 % road · 20 % motorway4,283 €2,067 €2,216 € · 420i
Long-distance10 / 40 / 5010 % city · 40 % road · 50 % motorway3,516 €1,914 €1,603 € · 420i

Cumulative saving for the 420i Convertible

1 year
2,216 €
3 years
6,649 €
5 years
11,082 €
10 years
22,164 €

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

What produces these figures

WLTP combined
10.7 L/100 km · 6.1 L/100 km
Powertrain
Combustion · Combustion
Power
350 ch · 184 ch
Kerb weight
1,355 kg · 1,690 kg

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Frequently asked questions

On a 100 km mixed trip, the BMW 420i Convertible is about 50% cheaper than the Porsche 718 Boxster S with default parameters. This ratio shifts with your actual energy prices - simulate for your profile.

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