PHEV consumption and the utility factor: why 1.2 l/100km is not your consumption
How the WLTP consumption figure of a plug-in hybrid is derived, what the utility factor is, and how to work out a more realistic figure yourself.
A plug-in hybrid with a WLTP figure of around 1.2 l/100km only consumes that under test assumptions. This guide explains how that figure arises and how you can derive a more usable number yourself. We make no recommendation and sell nothing.
How the PHEV WLTP figure is derived
The WLTP cycle for a plug-in hybrid weighs two states: driving with a full battery (largely electric, so little petrol) and driving with an empty battery (the car as a petrol engine carrying the battery weight). The low combined figure arises because the cycle assumes a certain share of electric driving. That weighted share is called the utility factor.
The utility factor in the WLTP test is an assumption, not a measurement of your behaviour. Charge every day and keep your trips within the electric range, and your actual petrol consumption comes close to the figure. Charge rarely and you are in effect driving a heavier petrol car: for the models in our catalogue, petrol consumption with an empty battery is closer to 6-7 l/100km (factory figure for petrol mode, indicative).
Why we show no efficiency score here
For PHEVs the efficiency score in the catalogue is often set to n.b.. That
is deliberate: a single figure that has to capture both the full-battery and
the empty-battery scenario would misrepresent reality for most drivers. We
prefer to show no figure rather than a misleading figure (see also the
guide on our reliability score
for the same line). The specs therefore list separately the electric range
(WLTP), the battery capacity and the petrol consumption in petrol mode.
Deriving a more realistic figure yourself
- Estimate honestly which part of your annual mileage falls within the electric WLTP range and starts with a fully charged battery. Call that share your own utility factor (for example 0.6 if 60% of your kilometres can be electric).
- Work out the remaining part using the petrol consumption in petrol mode from the specs.
- Add both parts weighted together. The result is almost always higher than the WLTP figure and lower than the pure petrol figure.
A worked example with catalogue figures: a PHEV with 60 km electric range WLTP and around 6.5 l/100km in petrol mode yields, at an own utility factor of 0.5, roughly 3-3.5 l/100km net fossil, not the 1.2 l/100km of the type plate. The electricity comes on top of that.
Indicative, no fiscal or financial advice. Always compare with an independent adviser and the official source.
Continue with the data: filter on fuel in the search engine, put a PHEV and a full hybrid side by side in the comparator, or look at the electric models if you would mostly drive electric.
No tax or financial advice. Every figure shows its source and reference date. Always compare with an independent adviser and the official source.