NOx Guide Reviewed 30 July 2026

VRT and NOx Calculator Ireland

See how the NOx charge is added to Irish VRT and why missing or high NOx figures can change an import estimate.

Quick answer

  • NOx applies to Category A vehicles excluding fully electric vehicles but including hybrids.
  • Revenue charges NOx per milligram per kilometre, with higher bands above 40mg and 80mg.
  • A NOx value shown in g/km is converted to mg/km by multiplying by 1,000.
  • Missing satisfactory NOx evidence can trigger €4,850 for diesel vehicles or €600 for other vehicles.
Calculator

Estimate Vehicle Registration Tax

Use the VRT Calculator Ireland page to estimate OMSP-based VRT, CO₂ component, NOx charge, EV relief and category-specific results.

OMSPRevenue market value CO₂ + NOxMain car inputs 2026Ireland estimate
Estimate VRT + NOx
On this page
  1. NOx charge bands
  2. NOx example visual
  3. Worked NOx calculations
  4. Where to find acceptable NOx evidence
  5. NOx, CO₂ and fuel type are different inputs
  6. Common NOx mistakes
  7. How NOx affects a total VRT estimate

NOx charge bands

NOx band Rate Why it matters
First 0–40 mg/km €5 per mg Lower-emission vehicles may stay mainly in this band
Next 40 mg/km up to 80 mg/km €15 per mg Costs rise quickly for moderate NOx values
Remainder above 80 mg/km €25 per mg High-NOx imports can become expensive
No satisfactory evidence Max diesel/non-diesel charge Documentation becomes critical before buying

NOx example visual

0–40mg€5/mg
40–80mg€15/mg
80mg+€25/mg

If a vehicle shows NOx as 0.090 g/km, convert it to 90 mg/km. The first 40mg is charged at the first rate, the next 40mg at the second rate, and the final 10mg at the third rate.

Worked NOx calculations

NOx evidence Band calculation NOx charge
0.008g/km = 8mg/km 8 × €5 €40
50mg/km 40 × €5 + 10 × €15 €350
90mg/km 40 × €5 + 40 × €15 + 10 × €25 €1,050
Diesel, no satisfactory evidence Revenue maximum €4,850
Petrol or other non-diesel, no satisfactory evidence Revenue maximum €600

The NOx rates are marginal. A 90mg figure is not multiplied entirely by €25: each portion is charged in its own tier.

Where to find acceptable NOx evidence

Revenue states that NOx is normally recorded on the Certificate of Conformity. Depending on the vehicle and documentation, the figure may also appear on a foreign registration certificate. The evidence must identify the vehicle and provide a usable emissions figure.

  • Check the Certificate of Conformity before paying a deposit.
  • Check both sides and all emissions fields on the foreign registration certificate.
  • Confirm whether the number is g/km, mg/km or—on a heavy-duty vehicle—mg/kWh.
  • Keep the original evidence for the NCTS registration appointment.
  • If the value is absent or unclear, resolve it before purchase rather than assuming a low charge.
Missing evidence is not the same as zero emissions.

Selecting zero in a calculator when the document is blank can understate the estimate by thousands of euro on a diesel vehicle.

NOx, CO₂ and fuel type are different inputs

Input What it measures How VRT uses it
CO₂ Carbon dioxide emissions Selects the Category A percentage band
NOx Nitrogen oxide emissions Creates a separate charge added to the CO₂ component
Fuel type Petrol, diesel, hybrid, plug-in hybrid or electric Affects NEDC conversion and the missing-evidence maximum; full electrics are excluded from NOx

A car can have a moderate CO₂ band and still attract a high NOx charge. Older diesels are especially worth checking before import because their NOx value or missing documentation can change the economic decision.

Common NOx mistakes

  • Entering g/km as mg/km without converting—or multiplying an mg/km figure by 1,000 again.
  • Applying the highest marginal rate to the entire NOx value.
  • Assuming hybrids or plug-in hybrids are exempt from NOx.
  • Entering zero when the document does not provide a figure.
  • Buying before checking whether the Certificate of Conformity includes a usable NOx value.
  • Ignoring the €4,850 diesel maximum when documentation is missing.

How NOx affects a total VRT estimate

For a Category A car, the NOx result is added after calculating the CO₂ component. For example, a €12,000 OMSP car at the 17.5% band has a €2,100 CO₂ component. If satisfactory NOx evidence is missing on a diesel, the €4,850 maximum would bring the planning total to €6,950.

This is why the calculator keeps the CO₂ and NOx components separate in the result. You can see whether the cost is being driven mainly by the Revenue market value, the CO₂ band or the emissions evidence.

Frequently asked questions

Is NOx included in VRT?

Yes. NOx is a component of VRT for relevant Category A vehicles.

Do electric cars pay NOx?

Fully electric vehicles are excluded from the NOx charge.

Do hybrid cars pay the NOx charge?

Yes. Revenue says the charge applies to Category A vehicles excluding electrics but including hybrids.

What if my diesel has no NOx figure?

If satisfactory evidence cannot be provided, Revenue publishes a maximum diesel charge of €4,850.

Is 0.090g/km the same as 90mg/km?

Yes. Multiply the g/km figure by 1,000, so 0.090g/km becomes 90mg/km.

How do I convert g/km to mg/km?

Multiply the g/km number by 1,000. For example, 0.008 g/km is 8 mg/km.

Sources & references

Back to VRT & Vehicle Import Ireland
How Is VRT Calculated in Ireland? Understand how Vehicle Registration Tax is estimated in Ireland using vehicle category, OMSP, CO₂ emissions, NOx and EV relief. VRT on Electric Cars Ireland 2026 Understand 2026 VRT relief for qualifying electric cars in Ireland, the €5,000 maximum, OMSP thresholds and electric motorcycle exemption. VRT Statistical Code Explained Understand why some VRT tools ask for a statistical code or registration number and why Irish Calculators uses a manual estimate instead.

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