Car CO2 Emissions: Ultimate Guide (2025 Update)

Do you know what the CO2 emissions are for your car? If not, do you know where you can find the information? Understanding your car’s emissions is important. Not only do they let you know how much road tax you’ll have to pay, but CO2 emissions have a direct link to fuel efficiency too.

If you don’t know our WLTP from your RDE, your CO2 emissions from your Euro 6 Standards emissions or, if your car is London ULEZ compliant, then this guide is for you.

CO2 rules and laws — Countries across the globe have pledged to reduce CO2 emissions

CO2 car emissions explained:

What are CO2 emissions and why do they matter?
CO2 emissions legislation in the EU and UK
What is Euro 6?
Did Brexit impact the legislation?
How is a car tested for CO2 emissions?
CO2 emissions tables for car tax
Where do I find the CO2 emissions rating for my car?
How can I reduce my car’s CO2 emissions?

What are CO2 emissions and why do they matter?

Carbon dioxide (CO2) emissions are produced naturally by decomposition, ocean release, and respiration. These natural levels are kept in balance by the ecosystem of the planet as CO2 is reabsorbed in a natural cycle.

However, CO2 is also produced by human activities and the burning of fossil fuels for heating, industry, and transportation. These man-made emissions increase the CO2 levels and upset the natural balance. This could cause possibly irreversible damage to the earth and its atmosphere, known as climate change.

To try and combat climate change, countries all over the world have come together to collectively pledge to take action. Part of this includes significantly reducing the CO2 emissions from cars and other vehicles.

CO2 emissions legislation in the EU and UK

Transportation is one of the highest contributors to emissions, responsible for around 33% of CO2 emissions in the UK, and 30% across Europe. To try and reduce these levels, the European Commission and industry associations of carmakers agreed to reduce the emissions on any new cars built.

> The first target in 2009 was to cut average car emissions to 140g/km of CO2.
> In 2015, this target reduced to 130g/km of CO2
> The goal for 2021 is for 95g/km of CO2

CO2 emissions are measured by weight, in grams (g) and calculated by how much CO2 is emitted from the exhaust pipe per the distance driven, measured in kilometres (km). CO2 emission rates are usually displayed as (g/km).

A new cars for sale now have to display a label displaying their fuel consumption and CO2 emissions. Anyone purchasing a new vehicle should look out for it and report if it’s missing.

Tackling CO2 emissions has the immediate goal of clearing up polluted air, and the ultimate goal of reducing the effects of climate change. Car emission regulations include Euro 6 standards as part of the European Commission’s air quality directive.

Euro 6 standards — All new cars must meet Euro 6 emissions standards

What is Euro 6?

Exhaust gases from cars contribute to air pollution, especially in concentrated urban areas. In addition to CO2, cars also emit the following pollutants:

> CO – carbon monoxide
> NOX – oxides of nitrogen
> PM – particulate matter (soot from diesel cars)
> HC – hydrocarbons

Cars with higher standards for emissions levels can be identified as they will score at least a Euro 6 level based on the European frameworks. Air pollutant emissions data is displayed on cars for sale alongside the CO2 data. CO2 data can be used as a direct comparison between cars, but air pollutant emissions data cannot.

Did Brexit impact the legislation?

Following Brexit, the UK is no longer bound by EU laws and regulations, including those related to emissions. However, the UK government has stated its commitment to maintaining environmental standards post-Brexit.

The UK has its own domestic legislation related to emissions and environmental protection. The UK government announced plans to ban the sale of new petrol and diesel cars and vans by 2035 as part of its efforts to reduce greenhouse gas emissions and tackle climate change. This initiative is part of a broader plan to achieve net-zero carbon emissions by 2050.

How is a car tested for CO2 emissions?

When a car or vehicle burns petrol or diesel, CO2 is emitted from the exhaust pipe. These emissions are measured during the testing of new car models and during a vehicle’s annual MOT test.

Emissions testing for new cars used to be done through the New European Driving Cycle (NEDC) rating, which was based on theoretical driving calculations. However, after the emissions testing scandals of VW and others, stricter standards were set.

On 1st September 2018, the Worldwide Harmonised Light Vehicle Test Procedure (WLTP) was introduced to measure emissions more accurately. This upgrade of the testing system has caused significant disruption in the car industry due to downgraded results for most car model ratings with lower fuel economy and higher emissions reported.

Cars are now examined over a longer distance, at higher speeds, and in different driving conditions for a more accurate representation of driving. Variables like faster acceleration, sharper braking, roof racks, and alloy wheels are also taken into consideration.

For true and accurate test results, cars are selected at random from the manufacturing line to ensure they can’t be ‘prepared’ for testing.

The Real Driving Testing (RDE) is also being used to supplement the laboratory-based WLTP results. This means vehicles are tested on a public road to get the best real-life emissions results. RDE measures NOx, particulate matter, carbon monoxide, and hydrocarbon emissions.

It’s not just new cars that are tested for their levels of emissions. Emissions are tested annually during the MOT test and your car will fail if emissions are higher than the standard set for the age of your vehicle.

On 20th May 2018, diesel cars had a new rule introduced in regards to MOT emissions testing. The standard for the car is dictated by the listing on the manufacturer’s plate. If the car emissions are not listed on the plate, then the car is tested to the default level for its age.

Roadside checks can be made to measure emissions. There is an allowance of 10 days to fix high emissions if your car fails. If the emissions are exceptionally high, then you will not be able to use the vehicle until it is fixed.

CO2 tax — Cars valued over £40,000 now have to pay an extra £320 a year for car tax

CO2 emissions tables for car tax

Since 2001, car tax has been charged based on a specific model’s CO2 emissions, not engine size. This has become more complicated in recent years as rates now vary depending on when the car was registered:

Cars registered before 1st March 2001

If your car was first registered before 1st March 2001 then the tax rate is based simply on engine size.

The current rate for engines up to 1549cc is £200.00 per year. The current rate for engine sizes over 1549cc is £325.00 per year.

Vehicles from this period that will still be on the road in 2025 are highly likely to be subject to further emissions regulations, as they are likely non-compliant with the UK’s Clean Air Zones (CAZs).

For a complete breakdown of tax rates, read our online car tax guide.

Cars registered between 1st March 2001, and 31st March, 2017

Older cars that were first new between 2001 and 2017 pay a standard VED rate annually based on their emissions.

The pricing goes up with emissions, with standard family cars from this period typically emitting at least 125g/km of C02, and SUVs and other large vehicles emitting even more.

In 2025, all cars emitting fewer than 110g/km of C02 will start to pay the current lowest petrol and diesel rate of £20 in VED per year.

These rates are still subject to change, and since vehicles in this category will be on the older side by 2025, they may end up subject to further charges based on emissions and efficiency compliance.

For a complete breakdown of tax rates, read our online car tax guide.

Cars registered between 1st April, 2017 and 31st March, 2025

New cars registered between the April 2017 tax year and the end of the 2024/25 tax year pay VED rates ranging from £0 to £2,605 depending on their emission outputs.

In the tax year beginning April 2025, cars first registered between 2017 and 2025 will be taxed differently, as follows:

Zero-emission vehicles will start paying a standard rate of £180 annual VED, losing their discount
Zero-emission vehicles originally worth over £40,000 will start paying the expensive car supplement if they are still under seven years old, until their seventh year from first registration (e.g. an expensive EV bought new in the summer of 2019 will be liable to pay for one year, whereas an expensive EV bought new in the summer of 2024 will be liable to pay from its second through to its seventh year)
It’s possible that the current first-year tax rates across all emissions levels change again.

For a complete breakdown of tax rates, read our online car tax guide.

Cars registered on or after 1st April, 2025

From 1st April, 2025, the VED rates for all new cars will be simplified into two categories in the first year, and one standard rate for all cars that’s payable from the second year onwards. New EVs will start being liable for the expensive car supplement from April 2025 too, losing their green exemption they’ve enjoyed until now.

For a complete breakdown of tax rates, read our online car tax guide.

Where do I find the CO2 emissions rating for my car?

If you look in your V5C logbook for your car, the Euro standard emissions rating is listed there, e.g. Euro 5 or Euro 6. You can also find the fuel consumption and emissions information for new and used cars on TotalCarCheck. Here, you can enter your car registration and access a huge range of information about your vehicle in just a click of a button.

Once you have entered your reg and pressed the ‘Click to Check’ button, you’ll be taken through to a page of information about your car including the make, model and MOT status. To find your CO2 emissions, you can view the graph under ‘Road tax information’. If you want to find out your car’s Euro status, you will have to purchase a Gold report. This is a more thorough sweep of your car’s information and is available from £3.99. You can see your Euro status under the ‘Additional information’ section of your full vehicle report.

Drive smart — Making changes to how you drive will reduce your emissions

How can I reduce my car’s CO2 emissions?

Whatever the official emissions ratings of your car, reducing your CO2 emissions will benefit you and your car. You’ll get better performance, better fuel MPG and it will help the environment.

Selling your car?

Read about everything you need to know about how to sell your car with more guides here. There’s a lot to learn as Clean Air Zones and emissions standards in the UK change in the run up to 2035.