NOx Levy Guide Ireland

What is the NOx Levy?

The NOx levy is a surcharge applied to vehicles registered in Ireland from 1 January 2020 based on their nitrogen oxide emissions. It sits on top of your standard Vehicle Registration Tax and applies to diesel, petrol, and hybrid vehicles that emit measurable levels of NOx from their exhaust.

Revenue introduced the NOx levy as part of Ireland's broader strategy to reduce harmful air pollution. Nitrogen oxides — primarily NO and NO₂ — are produced during high-temperature combustion and contribute to smog, acid rain, and respiratory illness. Transport is one of the largest sources of NOx in Ireland, so taxing vehicles on this output pushes buyers towards cleaner models.

The levy is calculated by multiplying your vehicle's official NOx emission figure (in mg/km) by the rate set by Revenue. It is charged once at the point of registration or import and is non-recurring. If your car qualifies as fully electric (BEV) or has zero tailpipe NOx, you pay nothing on this line. However, plug-in hybrids and standard hybrids with combustion engines do attract the levy unless they produce zero measured NOx under test conditions.

It is important to note that the NOx levy is separate from CO₂-based VRT bands. Both are applied when registering a vehicle in Ireland, but they measure different pollutants and use different rate structures. Your final VRT bill will typically include the base VRT rate (driven by CO₂) plus the NOx surcharge, if applicable.

How NOx Emissions Are Measured

Vehicle manufacturers test NOx emissions during type-approval using standardised driving cycles. The resulting figure is expressed in milligrams of nitrogen oxides per kilometre driven (mg/km). This official figure is what Revenue uses to calculate the NOx levy.

There are two main test cycles you will encounter depending on when your vehicle was approved:

• NEDC (New European Driving Cycle) — the older test cycle used until 2017 for type-approval. NEDC figures tend to be lower than real-world results because the test is less demanding and does not reflect aggressive driving or varied road conditions.
• WLTP (Worldwide Harmonised Light Vehicle Test Procedure) — the current standard, mandatory for all new vehicles registered since September 2018. WLTP testing is more rigorous, uses a wider range of speeds and temperatures, and produces figures that more closely match real-world driving.

When you check your vehicle's Certificate of Conformity or registration documents, you will see the NOx value listed under "mass of pollutants." The value may be given in g/km or mg/km — if it is in g/km, multiply by 1,000 to convert to the mg/km format Revenue uses. For example, 0.065 g/km equals 65 mg/km.

Real-world NOx can differ significantly from the official test figure. Diesel vehicles with older after-treatment systems often emit far more NOx on Irish roads than the lab test suggests. This is one reason the levy exists — it incentivises manufacturers to bring genuinely clean vehicles to market rather than relying on test-cycle optimisation alone.

NOx Levy Rates 2026

Revenue applies a flat rate per mg/km of NOx. The current rate, unchanged since the levy's introduction, is €7.50 per mg/km. The table below shows how this translates across common NOx emission levels:

There is no maximum cap on the NOx levy. If your vehicle has particularly high emissions, the levy can run into thousands of euros. This is why checking NOx before purchasing an imported vehicle is essential — a car that looks cheap on the forecourt can become expensive once VRT, customs duty, and the NOx surcharge are all added up.

For pre-2020 vehicles, the NOx levy does not apply at all. If you are importing a car first registered before 1 January 2020, you will only pay the standard VRT based on CO₂ emissions and the vehicle's open market selling price.

How to Find Your Car's NOx Emissions

Finding your vehicle's official NOx figure is straightforward if you know where to look. The value you need is the mass of nitrogen oxides expressed in mg/km, as this is what Revenue uses directly in the levy calculation.

Primary Sources

• Certificate of Conformity (CoC) — this manufacturer-issued document lists all type-approval data including NOx emissions. If you are importing from the UK or EU, request the CoC from the seller or the manufacturer's local distributor.
• Vehicle Registration Certificate — in Ireland, the NOx figure appears on the registration certificate issued by Revenue. For UK imports, check the V5C logbook section D2.
• Manufacturer website or dealer — many manufacturers publish full type-approval data online. Check the specs page for the specific model year and engine variant.

NEDC vs WLTP — Which Figure Applies?

Revenue accepts the figure from whatever test cycle the vehicle was type-approved under. For vehicles registered before September 2018, this is typically NEDC. For newer vehicles, it will be WLTP. The key point is that the figure on your official documentation is the one Revenue uses — not a conversion or estimate you calculate yourself.

If your documentation only shows NOx in g/km, convert it by multiplying by 1,000. For example, if the CoC states 0.042 g/km, the mg/km figure is 42 mg/km.

What If You Cannot Find the NOx Figure?

If your documentation does not include a NOx value — which can happen with older imports or vehicles with incomplete paperwork — Revenue applies a default cap. The default NOx values are:

• Diesel vehicles: 114 mg/km (resulting in an €855 levy)
• Petrol vehicles: 90 mg/km (resulting in a €675 levy)

These default figures are often higher than the actual NOx of modern vehicles. If you can obtain proper documentation showing a lower figure, you will almost always save money on the levy. Always request the Certificate of Conformity before finalising a purchase.

NOx Levy Worked Examples

Below are three realistic scenarios showing how the NOx levy is calculated for different vehicles being registered in Ireland in 2026.

How to Reduce Your NOx Levy

While you cannot change a vehicle's official NOx figure, there are several strategies to minimise or eliminate the NOx levy when importing into Ireland.

1. Choose a Vehicle with Low NOx

The most direct approach is selecting a vehicle with documented low NOx emissions. Modern diesel vehicles with Euro 6d or Euro 6d-temp approval typically produce 30–60 mg/km. Petrol vehicles are generally in the 10–50 mg/km range. Fully electric vehicles produce zero NOx and pay no levy at all.

2. Always Obtain the Certificate of Conformity

This single step can save you hundreds of euros. Without the CoC, Revenue must apply the default cap — 114 mg/km for diesel or 90 mg/km for petrol. Most modern vehicles actually emit less than these defaults, so having proper documentation usually results in a lower levy.

3. Consider a Petrol or Hybrid Alternative

If you are choosing between a diesel and a petrol version of the same model, the petrol variant will usually attract a lower NOx levy. Plug-in hybrids (PHEVs) can also be advantageous if they operate in electric mode frequently and have low official NOx figures, though this varies by model.

4. Go Fully Electric

A zero-emission vehicle eliminates the NOx levy entirely. Combined with reduced VRT rates and potential SEAI grants, a fully electric import can be the most tax-efficient option in Ireland's current system.

5. Check Before You Buy

Use our NOx VRT Calculator to estimate the total cost including the NOx surcharge before committing to a purchase. Comparing two similar vehicles with different NOx figures can reveal thousands of euros in difference at the point of registration.

NOx vs CO₂ — What's the Difference?

Both NOx and CO₂ are exhaust emissions, but they measure entirely different things and are taxed separately in Ireland's VRT system. Understanding the distinction helps you make informed purchasing decisions.

The key takeaway is that a vehicle can score well on one metric and poorly on the other. A diesel car might have very low CO₂ (good for the CO₂-based VRT) but higher NOx (bad for the NOx levy). Conversely, a petrol sports car might have high CO₂ but low NOx. When calculating the total registration cost in Ireland, you need to consider both factors together.

This is why our VRT Calculator accounts for both CO₂ bands and the NOx surcharge in a single calculation, giving you the true total cost of registering any imported vehicle.

Frequently Asked Questions

Calculate Your NOx Levy

Ready to work out the exact NOx surcharge for your vehicle? Use our free calculators to get an instant estimate: