When filling out an online registration form or declaring mileage expenses, we often find ourselves stuck on the same field: the number of fiscal horsepower. On a Peugeot 308, this figure varies significantly from one engine type to another, and choosing the wrong line can skew the amount of regional tax or insurance.
Read box P.6 of your 308’s registration certificate
The most straightforward method is to flip over the registration certificate. The fiscal horsepower is listed in box P.6, expressed in CV (fiscal horsepower). On a French certificate, this box is found in the technical block, just after the maximum net power (P.2) expressed in kilowatts.
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This value is often confused with DIN horsepower, which measures the actual mechanical power of the engine. DIN horsepower appears in box P.2 (converted to kW). Fiscal horsepower, on the other hand, is a purely administrative unit used by the State to calculate registration tax.
If you want to know how many fiscal horsepower for a Peugeot 308, the answer directly depends on the version and energy type: the differences range from 4 CV for the electric e-308 to 10 CV for the most powerful plug-in hybrid.
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Fiscal horsepower by engine type: the concrete differences on the 308
Not all 308s fit into the same fiscal category. Here are the values recorded on recent technical sheets:
- The 1.2 PureTech 130 hp and 1.5 BlueHDi 130 hp versions display 7 fiscal horsepower, just like the 1.2 Hybrid 136 hp (mild hybrid).
- The 308 plug-in hybrid 180 hp rises to 8 fiscal horsepower, a notch higher despite a more modest thermal engine than some gasoline trims.
- The PHEV 225 hp version climbs to 10 fiscal horsepower, which significantly increases the regional tax.
- The e-308 100% electric drops to 4 CV, thanks to the absence of CO2 emissions in the calculation formula.
One point to remember: the mild hybrid does not change the fiscal horsepower compared to the equivalent gasoline version. On the 2024 sheets from L’Argus, the 1.2 Hybrid 136 hp remains at 7 CV, exactly like the PureTech 130 hp. The mild electric assistance does not factor into the administrative calculation.
Calculation formula for fiscal horsepower: what box P.6 indicates
Since July 1998, fiscal horsepower in France has been calculated using the following formula:
PF = (CO2 / 45) + (P / 40) raised to the power of 1.6
PF represents fiscal horsepower, CO2 the emissions in grams per kilometer, and P the engine power in kilowatts. The result is rounded to the nearest whole number.
This formula explains why the electric e-308 drops to 4 CV: its official CO2 emissions are zero, and only the engine power comes into play. Conversely, the PHEV 225 hp combines high power and emissions (even low) that raise the total.
Why recalculating yourself is not always reliable
The official formula uses the manufacturer’s homologation values, not those displayed in commercial brochures. Variations of a few grams of CO2 between the mixed WLTP cycle and the value used for fiscal calculation can shift the result by one CV. For a used 308, the technical sheet by model year is more reliable than a manual calculation. L’Argus precisely displays the fiscal horsepower column by version for the 2021 and 2024 308s.
Fiscal horsepower of the 308 and cost of the registration certificate
The number of fiscal horsepower determines the amount of regional tax, which represents the largest portion of the registration certificate price. Each region sets a rate per fiscal horsepower, and the difference between 7 CV and 10 CV can represent several dozen euros on the registration certificate.
The impact doesn’t stop there. Two other factors vary according to fiscal horsepower:
- The kilometric scale used for declaring actual expenses to the tax authorities directly depends on the number of fiscal horsepower. A vehicle with 7 CV does not qualify for the same ceiling as a vehicle with 4 CV.
- Insurance companies incorporate fiscal horsepower into their pricing grid. Moving from 7 to 10 CV on a 308 PHEV 225 hp raises the premium, even if the driving profile remains the same.
- For company vehicles, the company vehicle tax (formerly TVS) also takes fiscal horsepower into account in certain scenarios.
Special case of imported 308s
On a Peugeot 308 purchased abroad, the fiscal horsepower does not appear on the European Certificate of Conformity (COC). This document mentions the power in kW and CO2 emissions, but not the fiscal horsepower, which is a specifically French unit. You must then apply the official formula or refer to the French technical sheets of the same model year to obtain the correct value before initiating the registration request.
The fiscal horsepower of a Peugeot 308 can be read in seconds on the registration certificate, box P.6. For a check before purchase or in case of doubt about a used model, the technical sheets by year and engine type provide the exact answer without resorting to an approximate calculation. In this generation, the difference between 4 and 10 fiscal horsepower depending on the engine type has a concrete impact on the registration certificate budget, insurance, and mileage expenses.