April 13, 2026 in United Kingdom — With diesel vehicles facing additional charges and higher road tax rates in some cases, many buyers wonder whether a petrol or diesel car is cheaper to tax. This guide provides a direct comparison of VED costs between petrol and diesel vehicles, including the diesel supplement and first-year rates, to help you decide which fuel type saves you money on road tax.
The Diesel Road Tax Question
Diesel vehicles typically have lower CO2 emissions than equivalent petrol engines due to better fuel efficiency — but road tax is based on CO2, not fuel type, so this advantage is reflected in the VED band. However, diesel vehicles face two additional cost considerations that do not apply to petrol: the diesel vehicle excise duty supplement and higher first-year VED for some diesel vehicles.
The Diesel VED Supplement
Diesel vehicles registered from April 1, 2018 onwards pay a £15 supplement on their first-year VED rate. This applies to all diesel vehicles (cars and light goods vehicles) first registered from that date. The supplement is only on the first-year rate — subsequent years use the standard annual rate with no supplement.
For example, a diesel vehicle in the 131-150g/km band pays £145 (first year rate) plus £15 supplement = £160 for year 1. A petrol vehicle in the same band pays £145 for year 1. From year 2 onwards, both pay £445/year with no difference.
VED Comparison: Same CO2 Band, Petrol vs Diesel
At the same CO2 emission level, the road tax difference between petrol and diesel is minimal after the first year:
| CO2 Band | Year 1: Petrol | Year 1: Diesel (+£15 supplement) | Years 2+: Both |
|---|---|---|---|
| 0-50 g/km | £0 | £0 (EV/hybrid) | £195/yr |
| 51-75 g/km | £0 | £0 + £15 = £15 | £205/yr |
| 76-90 g/km | £10 | £10 + £15 = £25 | £235/yr |
| 91-100 g/km | £10 | £10 + £15 = £25 | £265/yr |
| 101-110 g/km | £10 | £30 + £15 = £45 | £285/yr |
| 131-150 g/km | £130 | £130 + £15 = £145 | £445/yr |
| 151-165 g/km | £195 | £195 + £15 = £210 | £600/yr |
| 166-175 g/km | £245 | £245 + £15 = £260 | £600/yr |
| 176-180 g/km | £255 | £255 + £15 = £270 | £600/yr |
Where Diesel Often Has Lower Road Tax
Diesel vehicles often fall into lower CO2 bands than equivalent-performance petrol vehicles because diesel engines are more fuel-efficient. A modern diesel family SUV emitting 140g/km may have the same road tax as a petrol version of the same model at 160g/km — but the diesel pays less. The £15 first-year supplement does not offset the CO2 efficiency advantage.
Premium Supplement: Diesel vs Petrol for High-Value Vehicles
For vehicles over £40,000 list price (registered April 2017 onwards), the premium supplement of £410/year applies in years 2-5. This applies equally to petrol and diesel vehicles at the same CO2 band — there is no diesel-specific premium supplement beyond the first year £15.
Company Car BiK: Diesel vs Petrol
For company car drivers, diesel vehicles historically had a BiK tax advantage due to lower CO2 emissions. However, as the emission gap has narrowed and diesel BiK rates are now equal to petrol at the same CO2 level, this advantage has disappeared. The BiK rate is based purely on CO2, not fuel type.
5-Year Road Tax Comparison: Real-World Example
Compare a diesel and petrol version of the same family SUV (e.g., a diesel at 140g/km vs a petrol at 165g/km):
- Diesel (140g/km, pre-2018 registration): No first-year supplement. Years 2-5: £445/year. Total 5yr: £1,800
- Petrol (165g/km, pre-2018 registration): No first-year supplement. Years 2-5: £600/year. Total 5yr: £2,400
- Difference: Diesel saves £600 over 5 years — but consider fuel costs, tax differentials (vehicle excise duty), and other ownership costs
When Petrol May Be Cheaper to Tax
Petrol can be cheaper to tax when:
- The diesel vehicle is in a higher CO2 band than the petrol equivalent (e.g., a heavy diesel SUV vs a lighter petrol hatchback)
- The diesel vehicle was first registered April 2018 onwards and carries the £15 first-year supplement
- The diesel vehicle is over £40,000 list price (premium supplement applies to both but diesel may be in a higher band)
Key Takeaway: CO2 Band Is Everything
The fuel type (petrol or diesel) does not directly determine road tax — the CO2 emission level does. A low-emission diesel (£195/year from year 2) is far cheaper to tax than a high-emission petrol (£755/year from year 2). Choose the vehicle with the lower CO2 emissions regardless of fuel type. Use GOV.UK VED rate tables to compare the specific vehicles you are considering.
Conclusion
Road tax for petrol and diesel vehicles is determined by CO2 emissions — not fuel type. The only diesel-specific additional cost is the £15 first-year supplement for vehicles registered from April 2018 onwards. In practice, diesel vehicles often fall in lower CO2 bands than equivalent petrol vehicles, making diesel cheaper to tax overall. The £15 supplement is marginal compared to the CO2-based VED differences between vehicles. Always check the specific CO2 band for the exact vehicle, not just the fuel type.