Plug-in hybrids: real-world vs official fuel consumption

The short answer

• In real-world use, a private plug-in hybrid uses about 2.5 times its official figure, and a company one about 4.8 times.
• The European Commission confirms it with consumption data recorded by the cars themselves: for those registered in 2021, real-world emissions were 3.5 times the official ones.
• If you charge it every day and your trips fit within its electric range, it uses very little fuel.
• If you can’t charge at home or at work, it will use as much as a petrol car: the official figure means nothing to you.

Why the official figure is so low

In the type-approval test (WLTP), a plug-in hybrid is measured with a charged battery and with an empty one, and the two results are combined using a “utility factor”: the share of distance it’s assumed to drive on electricity, based on its range. The longer the range, the more electric driving the test assumes and the lower the official figure.

The problem is that on the road they’re charged far less than the test assumes. According to Fraunhofer ISI and the ICCT, using data from about 9,000 plug-in hybrids in Europe, private owners drive 45–49% of their distance on electricity, and company cars only 11–15%. The EU is correcting the utility factor to match these data.

What real-world data show

New cars in the EU have a meter that records the fuel and electricity it uses (OBFCM). Using those data, the European Commission found that for the 320,000 plug-in hybrids registered in 2021, real-world CO₂ emissions were 3.5 times the official values: 99 g/km more. For those registered in 2022, the relative gap rose from 249% to 314%, even though they had bigger batteries and longer range.

CO₂ emissions and fuel use go hand in hand: if a plug-in hybrid emits 3.5 times the official figure, it also uses about 3.5 times the official fuel. The Commission puts it down to them “not being charged and driven electrically as frequently as anticipated”. For petrol and diesel cars the gap is much smaller, around 20%: see real-world vs official fuel economy.

What it costs depending on how often you charge

As an example we take a plug-in hybrid SUV, the Kia Sportage PHEV. According to fueleconomy.gov, it uses about 24.9 kWh/100 km on electricity and, with an empty battery, about 6.7 L/100 km of petrol (35 US mpg, 42 UK mpg). We work out the cost of 15,000 km (9,300 miles) a year depending on the share of electric driving.

Never charging it costs about €1,692 a year. Charging it like a typical private owner, about €1,336, and with 80% electric driving, about €1,087. Charging at home on an off-peak tariff is cheaper than the average price in the table, and at a public rapid charger it’s more expensive.

Tips

• Before buying one, work out how much of your driving fits within its electric range and whether you can charge at home or at work. If the answer is “not much” or “no”, you won’t benefit from what makes it save fuel. Compare with a regular hybrid.
• Charge it every night, even if you haven’t used the whole battery, and use electric mode in town, where it saves the most.
• To find out what your plug-in hybrid really uses, go by the trip computer average over several weeks or by what you put in the tank, not by the spec sheet.
• The calculator doesn’t model plug-in hybrids, because their fuel use depends on how often they’re charged. To work out the cost of a trip, choose “My real figure” and enter the one you measure. On a long trip where the battery runs out early, use the empty-battery figure: work out your real mpg.

Frequently asked questions