How to check a car's CO2 emissions (g/km) by registration

How to check a car's CO2 emissions by registration

The fastest free route is the official DVLA Vehicle Enquiry Service. Enter the registration and it returns the vehicle's tax status, fuel type, engine size and its official CO2 emissions in g/km, drawn from the record created when the car was first registered.

Any reputable car-check tool that reads DVLA data by reg will show the same CO2 figure, often alongside fuel type, year and tax band, so you can read it in one place. The number itself originates from DVLA, so it should match whichever tool you use.

If a listing or seller quotes a different CO2 number to the DVLA record, trust the DVLA figure for tax and tax-band purposes. Sellers sometimes quote a manufacturer brochure figure or a different trim's number, which can differ from the value actually registered against that specific car.

• Have the registration (number plate) ready
• Use the DVLA Vehicle Enquiry Service or a check that reads DVLA data by reg
• Read the CO2 figure in g/km, plus fuel type and tax status
• Treat the DVLA-held figure as the one that sets road tax

Where the official CO2 figure comes from

The CO2 figure is not measured on your driveway. It is produced in a standardised laboratory test before the model goes on sale, then recorded against each car when it is first registered. Cars registered from around 2017 to 2018 onwards use the WLTP test (Worldwide Harmonised Light Vehicle Test Procedure), which was introduced to better reflect real-world driving than the older NEDC test it replaced.

Because the test method changed, you cannot always compare CO2 figures across different ages of car directly. A pre-WLTP car and a WLTP car with the same headline g/km were measured differently, so the newer figure tends to be the more realistic of the two.

Pure electric cars have an official CO2 figure of 0 g/km, because they produce no tailpipe CO2. Plug-in hybrids show a low lab figure that assumes a charged battery, so their real-world CO2 can be much higher if the car is rarely plugged in. The registered figure is still the one used for tax.

Why CO2 matters: road tax, ULEZ confusion, and company-car BIK

For cars first registered between March 2001 and March 2017, CO2 directly sets the annual road tax band: lower g/km means a cheaper band, and the lowest-emitting cars in this era can be very cheap or free to tax. For cars registered from April 2017 onwards, CO2 sets the first-year showroom rate only, after which most cars move to a flat standard rate from year two.

The first-year rate is strongly CO2-linked. From 1 April 2025 it ranges from a token amount for zero-emission cars up to around 5,490 pounds for the highest-CO2 models (255 g/km and above), so on a new or nearly new car the CO2 figure can mean a large one-off difference. Note that from April 2025 even zero-emission cars pay VED, and the expensive-car supplement applies to higher-list-price cars including EVs.

Here is the part people get wrong: CO2 is not what decides ULEZ or Clean Air Zone charges. Those zones target local air pollution (mainly NOx), so they are based on a car's Euro emissions standard, not its CO2. In practice that usually means Euro 4 for petrol (broadly 2006 onwards) and Euro 6 for diesel (broadly September 2015 onwards); London's ULEZ charge for non-compliant cars is 12.50 pounds per day. A low-CO2 older diesel can still be non-compliant, so check the zone rules separately rather than assuming a green CO2 figure means no charge.

• Road tax (VED): CO2 sets the band (2001-2017 cars) or the first-year rate (2017+ cars)
• Company-car tax: CO2 sets the Benefit-in-Kind percentage, so it directly affects monthly take-home pay
• Fuel cost proxy: higher CO2 broadly means higher fuel use and running costs
• ULEZ / Clean Air Zones: NOT decided by CO2 — these use the Euro emissions standard (NOx), so check those separately

CO2 and company-car (Benefit-in-Kind) tax

If you choose a company car, the CO2 figure has an outsized effect on what you pay. The taxable Benefit-in-Kind (BIK) is calculated as a percentage of the car's list price, and that percentage is set by the car's CO2 emissions, with the lowest rates reserved for zero and ultra-low emission cars.

This is why electric and low-CO2 plug-in hybrids are popular as company cars: a much lower BIK percentage can mean dramatically lower monthly tax for the driver compared with a high-CO2 petrol or diesel of similar value.

Before signing for a company car, check the exact registered CO2 figure rather than relying on a brochure band, because the BIK percentage and your monthly cost follow directly from it. HMRC publishes the current BIK percentage bands, so pair the registered g/km figure with the official table for an accurate estimate.

What a CO2 check does and does not tell you

A CO2 check is great for tax and running-cost questions, and the figure is free to look up by reg. But it is narrow: it tells you the lab CO2 in g/km and nothing about the car's condition, history or legal status. A low CO2 figure does not mean a car is roadworthy, honestly described, or free of finance or write-off history.

Be especially careful with two assumptions. First, low CO2 does not equal ULEZ or Clean Air Zone exemption, because those are based on the Euro standard, not CO2. Second, the absence of a problem in a free reg lookup does not prove a car is clean; free checks only show what the public DVLA and DVSA records hold, such as MOT history, recorded mileage and tax status.

We are upfront about this because it is our edge. The free checks on MOT Checkup show you the public-record facts: MOT test history and advisories, the mileage readings recorded at MOT, and current tax and SORN status. They do not, and cannot, confirm whether a car has outstanding finance, has been stolen, or was previously written off, that needs a separate paid provenance check against licensed insurance and finance data. So use CO2 for tax planning, use the free MOT, mileage and tax checks for condition and admin facts, and use a paid provenance report before money changes hands on a used car.

• CO2 tells you: lab emissions in g/km, your road-tax band and first-year rate, and your company-car BIK band
• CO2 does not tell you: ULEZ/CAZ status (that is the Euro standard), condition, mileage honesty, or hidden history
• Free checks (what we hold): MOT history and advisories, recorded mileage, tax and SORN status
• Needs a paid provenance check: outstanding finance, stolen markers, and write-off (Cat S / Cat N) history

Next step: check the figure that actually decides clean-air charges

Now that you have the CO2 figure for tax, the most common follow-up question is whether the car will cost you to drive in London or a Clean Air Zone, and that is a different number entirely. CO2 sets your tax; the Euro emissions standard sets your ULEZ and CAZ liability.

Use our free ULEZ checker to see whether a car meets the ULEZ standard by registration before you buy or drive into a zone, so you are not caught out by a daily charge. It is the natural companion to a CO2 check and it costs nothing.

After that, if you are buying the car, run the free MOT, mileage and tax checks to confirm the public-record facts, and consider a paid provenance report to cover finance, theft and write-off history that free checks cannot show. That sequence, CO2 for tax, ULEZ for charges, free checks for condition, paid report before payment, gives you the full picture without overpaying for data you do not need.