WLTP vs Real-World Fuel Consumption: Why Cars Use More

What WLTP measures

The Worldwide Harmonised Light Vehicles Test Procedure (WLTP) is run on a rolling road in a laboratory. For a normal passenger car, the test cycle (class 3) lasts 1,800 seconds and covers about 23.25 km. It has four phases:

The average speed is 46.5 km/h including stops. Each model is measured twice: once with standard equipment and once fully equipped, so that heavier options, bigger wheels and worse aerodynamics show up in the figure for that version.

For comparison, the old New European Driving Cycle (NEDC) lasted 20 minutes, covered 11 km at an average of 34 km/h and peaked at 120 km/h. WLTP is longer, faster and more dynamic, which is why WLTP figures are usually higher than the NEDC figures for the same car. Manufacturers had to certify new models under both tests from 1 September 2017, and from September 2018 only the WLTP figures were legally valid.

WLTP vs real-world fuel consumption: how big is the gap?

Since January 2021, every new car and small van sold in the EU must have an on-board fuel consumption monitoring (OBFCM) device that records the fuel or energy actually used. The European Commission published its first analysis of this data in March 2024, based on a sample of about 600,000 cars registered in 2021.

Fuel use and CO2 rise together, so the same percentages apply to litres per 100 km for petrol and diesel cars. The data covered only about 10.6% of the cars registered that year, and the Commission says monitoring must improve. Even so, it is the largest real-world sample available, and it comes from the cars' own sensors rather than from drivers' estimates.

Worked example: what the gap costs you

We calculated a 2026 example for a petrol car with an official WLTP figure of 5.5 l/100 km, driven 15,000 km a year, at an assumed price of €1.75 per litre in 2026.

Budget with the real-world figure, not the brochure one. Our fuel cost calculator prices any distance, and the fuel economy converter turns mpg figures from UK reviews into l/100 km.

Why plug-in hybrids miss their figures

A plug-in hybrid's official figure assumes it often runs on battery power. The test uses a so-called utility factor: an estimate of how much driving is done electrically. If the owner rarely charges, or drives long distances, the petrol engine does most of the work and carries the weight of the battery too.

The fleet data shows how far reality is from that assumption. The European Commission found real-world CO2 emissions of 2021 plug-in hybrids 3.5 times above the official values. Transport & Environment analysed European Environment Agency data for more than 800,000 plug-in hybrids registered from 2021 to 2023. It found an average of 139 g/km in real use against an official 28 g/km, and a gap close to five times for 2023 cars. Earlier research by Fraunhofer ISI in 2022 put real consumption at three to five times the WLTP values. The utility factor is being adjusted from 2025 to bring official figures closer to real use.

A plug-in hybrid can still be economical if you charge it every day and most of your trips fit within its electric range. If you cannot charge at home or work, a conventional hybrid or an efficient petrol car is usually the better choice. Our older article on hybrid cars and their types explains how the systems differ.

Electric cars: the same gap in range

The WLTP also sets the official range of electric cars, and it was a shock for some models when the test changed. Wikipedia's article on WLTP lists the official range of the Renault Zoé falling from 400 km under NEDC to 300 km under WLTP, 25% lower. The BMW i3 fell from 300 to 245 km (18% lower) and the Hyundai Kona 64 kWh from 546 to 482 km (12% lower). You can read more about these cars in our articles on the Renault Zoe Z.E. 40, the BMW i3 and the first-generation Hyundai Kona.

Real range then depends on the same things as fuel use, plus temperature. Motorway speeds and winter cold usually cut it the most, because cabin heating draws energy that the lab test does not ask for.

Seven reasons your car uses more than WLTP

1. Higher speeds. The WLTP spends only 323 seconds in its fastest phase, with a top speed of 131.3 km/h. Air resistance grows with roughly the square of speed, so a long motorway run at 130 km/h costs much more than the cycle suggests.
2. Cold starts and short trips. A cold engine uses more fuel, which is why the AA advises combining short trips into one journey.
3. Heating, air conditioning and other loads. Climate control, heated seats and screens and lights all take energy. The AA notes that air conditioning raises fuel use more at low speeds than at high speeds.
4. Roof boxes and racks. The German motoring club ADAC says a roof box adds about 11% at 80 km/h and about 2 litres per 100 km at 130 km/h.
5. Extra weight. ADAC puts the cost at up to 0.3 l/100 km for every extra 100 kg.
6. Tyres. Under-inflated tyres roll with more resistance. Natural Resources Canada, quoted by Wikipedia, estimates about 1% more fuel for every 0.1 bar drop in all four tyres. Wider optional wheels add rolling resistance too, which is one reason the WLTP measures fully equipped versions separately.
7. Driving style and traffic. Hard acceleration, late gear changes and stop-start traffic all push consumption up. ADAC says changing up too late alone can raise fuel use by about 30%.

How to measure your real consumption

The trip computer is a good start; reset it and compare similar periods, as the AA suggests. A simple cross-check is the full-tank method:

1. Fill the tank until the pump clicks off and reset the trip meter.
2. Drive normally until the tank is at least half empty.
3. Fill up again to the click and note the litres.
4. Divide the litres by the kilometres driven and multiply by 100 to get l/100 km.

Repeat it over several tanks and seasons. Winter figures will be higher than summer ones, and a holiday trip with a full car will differ from the daily commute. If you compare a figure with a review, check whether it was measured in summer or winter and at what speeds.

How to choose a car with realistic expectations

• Compare WLTP figures between cars, not with your own driving. The test is the same for every car, so it is fair for ranking models, even if the absolute numbers are optimistic.
• Add a safety margin. Use about +25% for a petrol car and +20% for a diesel as a starting point, based on the 2021 EU data, then adjust for your own driving.
• Be honest about charging. A plug-in hybrid only makes sense if you can plug in almost every day.
• Check the exact version. Larger wheels and heavier trims have their own WLTP figure. Look up the version you plan to buy in our car catalogue.