WLTP vs NEDC in Portugal: Why the CO₂ Figure on Your Documents Affects Your ISV

When Portugal calculates ISV — the vehicle registration tax — one of the key inputs is CO₂ emissions. For years, that figure came from NEDC testing. Since 2019, it increasingly comes from WLTP. The problem: WLTP typically produces higher CO₂ figures than NEDC for the same vehicle. And a higher CO₂ figure can mean a higher ISV band. Understanding which figure is on your vehicle's documents, and how AT uses it, can make a meaningful difference to your import cost estimate.

WLTP from Sept 201910–25% higher CO₂ than NEDCAffects ISV bandsCoC section 49.4

If your documents show both WLTP and NEDC CO₂ figures, enter the WLTP figure for a more conservative and usually more accurate estimate of your ISV.

Step 1 of 425%

Your Vehicle

What type of car are you considering?

CartaxPortugal.com — Free Portuguese vehicle tax calculator. Not affiliated with the Portuguese tax authority.

Based on published 2026 tables. Always verify with the Autoridade Tributaria for your specific situation.

What Is WLTP?

WLTP stands for Worldwide Harmonised Light Vehicle Test Procedure. It is the emissions and fuel consumption testing standard that replaced NEDC in the EU. WLTP was designed to produce more realistic figures by using:

WLTP became mandatory for all new EU vehicle type-approvals from September 2017 for new models, and from September 2018 for all new registrations. By September 2019, NEDC was effectively replaced for new vehicles across the EU.

What Was NEDC and Why Was It Replaced?

NEDC (New European Driving Cycle) was the EU's vehicle testing standard for decades. It was developed in the 1970s and last revised in the 1990s. Criticism of NEDC centred on its unrealistically controlled laboratory conditions — consistent speed, warm temperatures, no air conditioning, minimal electrical load — which produced CO₂ and fuel consumption figures that bore little resemblance to real-world driving.

The result was that NEDC figures were systematically optimistic. Most drivers found their actual fuel consumption significantly higher than NEDC advertised. The shift to WLTP was a regulatory acknowledgement of this gap.

How CO₂ Affects Portuguese ISV

ISV (Imposto Sobre Veículos) is calculated based on two main components: engine displacement and CO₂ emissions. Both components use graduated band structures — meaning higher displacement and higher CO₂ both result in higher ISV. The CO₂ component is particularly sensitive: crossing a band threshold has a disproportionate effect on the total ISV amount.

Because WLTP typically produces CO₂ figures 10–25% higher than NEDC for the same vehicle, a vehicle tested under WLTP may fall into a higher ISV band than the equivalent NEDC-tested vehicle. For illustrative purposes only, approximate impacts might look like this:

Vehicle typeTypical NEDC CO₂Typical WLTP CO₂Approx. ISV difference
Compact petrol (1.0T)~110 g/km~130 g/km€500–800
Mid-size petrol (1.5T)~135 g/km~155 g/km€1,000–1,500
SUV diesel (2.0D)~145 g/km~170 g/km€1,500–2,500
Plug-in hybrid~90 g/km~115 g/km€800–1,200

These figures are illustrative only. Actual ISV depends on your vehicle's exact CO₂, engine displacement, and age. Use the ISV calculator above with your vehicle's specific CoC data for an accurate estimate.

Which CO₂ Figure Does Portugal's AT Use?

Vehicles approved from September 2019

For vehicles with EU type-approval after September 2019, WLTP is the standard. The CoC will show a WLTP CO₂ figure in section 49.4. This is the figure AT uses for ISV calculation.

Vehicles approved before September 2019

For older vehicles, NEDC remains the applicable standard. Section 49.1 of the CoC contains the NEDC CO₂ figure. Section 49.4 may be absent or marked N/A.

Transition vehicles (2017–2019)

Some vehicles from the transition period carry both NEDC and WLTP figures on their CoC. In this case, AT typically applies the WLTP figure for vehicles from the 2019 model year onward. If you have a vehicle from this period and are uncertain which figure applies, confirm directly with AT — and use WLTP as your planning estimate.

Where to Find CO₂ on Your Documents

Certificate of Conformity (CoC)

The CoC is the authoritative source for ISV purposes. Find CO₂ in:

Use the "combined" or "weighted combined" figure, not the individual phase figures (low / medium / high / extra-high).

German vehicles

German CoCs follow the EU standard format. WLTP CO₂ in section 49.4 for post-2019 vehicles. The Fahrzeugbrief (Zulassungsbescheinigung Teil II) may also show CO₂ but the CoC takes precedence. See the Germany import guide for a full breakdown of German document requirements.

UK vehicles

UK V5C documents show CO₂ in g/km, but the format and figure may differ from the CoC. For ISV purposes, always use the CoC figure. Post-Brexit UK vehicles may have V5C figures that reflect UK testing standards rather than EU WLTP — another reason the CoC is preferred. See the UK import guide for context.

Electric Vehicles: A Special Case

Battery-electric vehicles have a CO₂ emissions figure of zero, regardless of testing standard. WLTP for EVs is relevant for energy consumption and range — not CO₂. For Portuguese ISV purposes, the zero CO₂ is what underpins the ISV exemption for BEVs. For plug-in hybrids, the WLTP CO₂ figure is very relevant — it determines which ISV band applies, and WLTP figures for PHEVs are typically significantly higher than their NEDC equivalents.

For full detail on EV and hybrid ISV treatment, see the EV import guide.

N1 Vehicles and CO₂

N1 vehicles (commercial vehicles under 3.5 tonnes GVM) are also subject to ISV, but under a different table (Table B). The CO₂ figure from the CoC — whether WLTP or NEDC — feeds into the Table B calculation. The WLTP vs NEDC distinction applies equally to N1 vehicles. For a full explanation of the N1 category and its ISV implications, see the N1 explained guide.

Practical Summary: Using the Right CO₂ Figure

  1. Find your vehicle's CoC
  2. Check section 49.4 for WLTP CO₂ (post-2019 vehicles)
  3. If section 49.4 is absent, use section 49.1 (NEDC)
  4. If both are present, use WLTP (49.4) as your estimate
  5. Enter that figure in the ISV calculator for your cost estimate
  6. If uncertain, contact AT directly with your CoC for confirmation
ISV band rates and thresholds are updated annually under Portugal's Finance Act. The CO₂ bands used for ISV calculation may change year to year. Always verify current rates with AT before relying on a specific estimate. CarTaxPortugal updates its calculator when rates change, but this page is for educational purposes and should not be treated as a definitive legal or tax guide.

For the full vehicle import process including document requirements and AT registration, see the main import guide. For IUC (annual road tax) and how CO₂ affects that calculation separately, see the IUC road tax guide.

Frequently Asked Questions

Does Portugal use WLTP or NEDC for ISV calculations?
Portugal's AT uses the CO₂ figure recorded in the vehicle's official documents — which will be WLTP for vehicles approved after September 2019, and NEDC for older vehicles. If your CoC shows both figures, WLTP is typically used for vehicles from the 2019 approval cycle onward. If you are unsure which applies to your vehicle, use the WLTP figure as the more conservative (and usually more accurate) estimate.
What if my vehicle documents only show a NEDC CO₂ figure?
If your vehicle was registered before September 2019 and only has a NEDC CO₂ figure, this is the figure AT will work from. The key implication is that older vehicles with only NEDC data may have a lower CO₂ figure than an equivalent vehicle tested under WLTP — which can result in lower ISV. This is not something you can control; it simply reflects the testing standard in use when the vehicle was approved.
Where do I find the WLTP CO₂ figure on my Certificate of Conformity?
On the EU standard Certificate of Conformity, WLTP CO₂ data appears in section 49.4 (combined WLTP cycle, in g/km). NEDC CO₂ data, where present, appears in section 49.1. If your CoC predates WLTP adoption, section 49.4 may be absent or marked 'N/A' — in which case, section 49.1 (NEDC) is the relevant figure.
Why is the WLTP CO₂ figure higher than NEDC for the same vehicle?
WLTP (Worldwide Harmonised Light Vehicle Test Procedure) was designed to produce more realistic emissions figures than the NEDC (New European Driving Cycle), which was conducted under controlled laboratory conditions that critics argued were too favourable. WLTP uses longer test distances, more varied speed profiles, and accounts for optional equipment weight. As a result, WLTP CO₂ figures are typically 10–25% higher than NEDC for the same vehicle — which can place a vehicle in a higher ISV band.
Does the CO₂ figure affect IUC (annual road tax) as well as ISV?
Yes. IUC calculation also factors in CO₂ emissions for most vehicle categories. A higher CO₂ figure under WLTP can therefore affect both the one-time ISV payment at registration and the ongoing annual IUC. The IUC impact is typically smaller in absolute terms than ISV, but it is worth factoring into your total cost estimate.
My car was registered in 2018 — which CO₂ figure does Portugal use?
For vehicles approved before September 2019, NEDC is the standard testing cycle. Your CoC and registration documents should show a NEDC CO₂ figure. If your CoC shows only NEDC data, AT will use that figure. If your 2018 vehicle happens to show both (some early dual-certification vehicles did), WLTP may be used — check the CoC sections 49.1 and 49.4.
How much can the WLTP vs NEDC difference actually affect my ISV?
The financial impact depends on your vehicle and how the CO₂ difference moves you across ISV bands. For a compact petrol car moving from 110g/km (NEDC) to 130g/km (WLTP), the difference can be €500–€800 in ISV. For a larger SUV moving from 145g/km to 170g/km, the difference can exceed €1,500–€2,500. The impact is non-linear because ISV uses graduated bands — crossing a band threshold has a disproportionate effect.
Do electric vehicles have a WLTP CO₂ figure?
Battery-electric vehicles have a CO₂ emissions figure of zero, regardless of testing standard. WLTP for EVs is primarily relevant for energy consumption and range, not CO₂. For Portuguese ISV purposes, a BEV's zero CO₂ is the relevant figure — and it is this zero figure that underlies the ISV exemption. For more detail, see the EV import guide.
What section of the CoC shows WLTP CO₂?
Section 49.4 of the EU standard Certificate of Conformity contains the WLTP combined CO₂ figure in g/km. This is the figure to use for ISV estimation purposes when present. Section 49.1 contains the NEDC figure where applicable. Some CoCs also show WLTP figures in sections 49.4.1 (low), 49.4.2 (medium), 49.4.3 (high) and 49.4.4 (extra-high) — use the 'combined' or 'weighted combined' figure for ISV estimation.
My UK V5C shows a different CO₂ than my CoC — which does AT use?
AT relies on the Certificate of Conformity as the primary technical document. If there is a discrepancy between the V5C (UK registration document) and the CoC, the CoC takes precedence. The V5C may show CO₂ in a different format, under different testing conditions, or with rounding differences. For any import calculation, use the CoC figure from section 49.4 (WLTP) or 49.1 (NEDC) as appropriate.

Related guides

→ Importing an EV to Portugal: ISV exemption and full process→ UK car import to Portugal after Brexit→ Portugal N1 vehicle category: ISV, Table B and homologation→ Importing a car from Germany to Portugal→ ISV Calculator Portugal→ IUC road tax in Portugal: rates and calculation→ Importing a car to Portugal: complete guide