Plug-In Hybrid vs Hybrid Labels Assume 25 Kilometres Between Charges

Don’t read the litres figure on a plug-in hybrid as the car’s appetite. Read it as a promise about your charging, made to an average driver who isn’t you.

That’s the trouble with any plug-in hybrid vs hybrid comparison done straight off the label. The single number is a blend of two test results, and the blend leans on a fixed distance of 25 kilometres written into the rule. Nothing in it knows how often you plug in. Put your own driving back into the sum and the answer moves, sometimes a long way in the plug-in’s favour and sometimes not at all.

This post shows where the figure comes from, then gives you the sum that turns a label into a number you can set against a plain hybrid’s. Every worked example is invented for illustration. It’s general information as at 26 August 2026, and no make, model or price appears, because the method works on any car’s label.

What the number on the label is

A plug-in hybrid sold in Australia has to carry an energy consumption label under the national labelling standard, Australian Design Rule 81/02. The label shows four things: energy consumption in watt-hours per kilometre, electric range, fuel consumption in litres per 100 kilometres, and carbon dioxide in grams per kilometre. On a plug-in, the fuel and CO2 values shown are the combined value, not a single test result.

A plain hybrid’s label is a different kind of number. It’s the measured result of the car running as a hybrid, with no second test blended in. That’s why a plain hybrid and a plug-in can sit side by side on a showroom page and look like a fair contest when they aren’t quite measuring the same thing.

There’s one more thing to check as at 26 August 2026, because two label regimes can be on a showroom floor at once. A newer standard, ADR 81/03, applies to new models first produced on or after 1 July 2026, and to every model from 1 July 2028. A vehicle that complies with 81/03 doesn’t have to comply with 81/02. So a car labelled under the older rules can stand beside one labelled under the newer. The Green Vehicle Guide’s fuel consumption label page, as published in June 2026, lists a “Test Cycle” field. NEDC means the older label, and WLTP means the newer one.

The sum in this post is built for the older label, so check that field first. And remember that a label figure is a headline number with a method behind it. Like the congestion cost figures this site has taken apart, it reads very differently once the method is on the table.

The 25 kilometres inside the formula

The test runs the car twice. In the first run the battery starts full, which the standard calls condition A. In the second the battery starts at its minimum state of charge, condition B. The label figure is a weighted average of the two results, and the weights are where the 25 kilometres lives.

The formula, in the standard’s own terms, is:

C = (De x C1 + Dav x C2) / (De + Dav)

C is the figure that ends up on the label. De is the electric range. C1 is the fuel result with a full battery, and C2 is the result with the battery at minimum charge. Dav is 25 km, which the instrument describes as the “assumed average distance between two battery recharges” (ADR 81/02, Compilation 8, Appendix C, Annex 8, paragraphs 3.4.4.1 and 4.4.4.1). For cars tested over repeated cycles the standard gives a second version that swaps the electric range for the OVC range, the total distance covered until the charge is depleted, and keeps the same 25 km (paragraphs 3.4.4.2 and 4.4.4.2).

For a plug-in with an operating mode switch whose electric range is longer than one complete test cycle, the manufacturer may ask, with the technical service’s agreement, to run the full-battery test in pure electric mode, which makes C1 zero (paragraph 4.2.1). In effect, the full-battery test is then treated as using no fuel at all.

Now read the formula as a weighting. The full-battery result is weighted by the electric range, and the minimum-charge result by the fixed 25. So the share of the blend that comes from the full-battery result is the electric range divided by that range plus 25. Table 1 works it out for four ranges.

Table 1: computed from the formula’s weights, De / (De + 25).

The longer the electric range, the more of the blend comes from the battery. A plug-in with a 100 km range puts 80 per cent of the weight on its full-battery result, and one with 30 km puts only 54.5 per cent. It’s the same formula and the same 25 km, and a different assumption about how the car is driven. You can read the weight as the share of your kilometres the label behaves as if it came off a charge, and the point to take from that is that the label for a plug-in isn’t a measurement of a car being driven by you but a weighted average built on an assumed distance, with weights that shift with electric range, so two plug-ins carrying the same label figure can rest on quite different assumptions about your week.

Work the label back to a hybrid-mode figure

If the label figure is a blend, the sensible move is to unblend it. With C1 taken as zero, the formula rearranges into one short line:

battery-flat figure = label fuel figure x (electric range + 25) / 25

Take a hypothetical plug-in, invented for this post and not any model. Its label shows 1.8 L/100 km and an electric range of 50 km. Working back, 1.8 x (50 + 25) / 25 is 1.8 x 3, which gives about 5.4 L/100 km. That’s your estimate of what the car uses when the battery is flat and the petrol engine is doing all the work.

Treat it as an upper-end estimate. The sum assumes C1 is zero. If a manufacturer reported a full-battery result above zero, the true battery-flat figure sits a little lower than the sum says.

Now the limits, stated plainly. This works for a car labelled under 81/02. Under 81/03 the label carries the same kinds of value: fuel consumption, tailpipe CO2, and for plug-ins the electric energy consumption and battery range. But the standard points to the UN R154 (WLTP) test, in which a “utility factor” sets the assumed electric drive share, and this post doesn’t summarise that factor. Don’t run the sum above on a newer label as though it were the older formula. Check the Test Cycle field first, and if it says WLTP, leave the unblending alone.

Plug-in hybrid vs hybrid at your own share of electric kilometres

Now set the battery-flat figure against a plain hybrid. Take a second hypothetical car, a plain hybrid at 4.5 L/100 km. Every figure in Table 2 is invented, and none of them is any real car’s.

Table 2: hypothetical figures, not any car. A hypothetical plug-in (label 1.8 L/100 km, range 50 km, battery-flat about 5.4) against a hypothetical hybrid at 4.5 L/100 km.

The rule behind the table is short. Take the battery-flat figure and multiply it by the share of your kilometres that still need petrol. At 20 per cent of kilometres from a charge, that’s 5.4 x 0.8, or about 4.3. The break-even against the 4.5 hybrid sits where 5.4 x (1 minus the share) equals 4.5, which is a share of about 16.7 per cent. Below that share the plain hybrid uses less fuel. Above it, the plug-in does. The bottom row is Table 1 again: 66.7 per cent is the weight a 50 km range puts on the full battery, and it’s why the label says 1.8.

Three hypothetical drivers show how far apart the outcomes sit. All three drive the same hypothetical plug-in for 270 km in a week.

• Driver A charges nightly and covers 200 km a week on the battery. That’s 74 per cent of the week, and fuel use works out at about 1.4 L/100 km, which beats the label.
• Driver B plugs in once a week and covers 50 km on the battery. That’s 18.5 per cent, and fuel use is about 4.4 L/100 km, level with the hybrid.
• Driver C never plugs in. Fuel use is the battery-flat 5.4 L/100 km, about 20 per cent above the hybrid.

One car, three outcomes, and the 1.8 on the label describes none of them. Litres are only half the story as well, since the price of a litre is a separate question that our piece on finding the cheapest petrol takes up and this post doesn’t.

What real driving does to the label

Put the sum against real-world data and the same pattern shows up. Fraunhofer ISI and the ICCT studied about 9,000 plug-in hybrids in Europe in a project reported in a press release dated 9 June 2022, drawing on drivers’ own fuel logs and fleet data. Private owners’ cars averaged between 4.0 and 4.4 L/100 km in use, against about 1.6 to 1.7 on the official test, with 45 to 49 per cent of their mileage electric. Company cars averaged between 7.6 and 8.4 L/100 km, with 11 to 15 per cent of their mileage electric.

Both groups used more fuel than the official figures, and the group with the smaller electric share used far more. The release also says the utility factor “defines the assumed electric drive share in WLTP”. That sentence is the European version of this post’s argument: a test-side assumption about how much of your driving comes off a charge.

Be fair about what that data is. It’s European, it covers plug-ins certified under both the older NEDC and the newer WLTP, and it’s self-reported through fuel logs and fleet data. No Australian equivalent is cited here, and nothing in this post claims to know what Australian owners get. What it does show is a gap between a test and a life, and tyre pressure and load are among the ordinary reasons a car’s fuel use departs from a test, which makes a tyre care routine relevant to fuel use too.

The fair case for the plug-in

The plug-in deserves a straight hearing. If you charge regularly and the electric range covers most of your daily distance, the label’s assumption is met or beaten. Driver A is the example: 1.4 against a label of 1.8, and far under the plain hybrid’s 4.5. For that driver the plug-in wins on fuel by a wide margin, and no amount of fine print changes it.

There’s an EV-first view too, and it’s a sound one for anyone whose daily pattern never needs petrol. A petrol engine you rarely use is a second powertrain you carry around without needing it. A reasonable person can run the sum, see their own share sitting near the top of Table 2, and decide a plug-in is a stepping stone they don’t need. Both readings are fair, and the sum is how you find out which one is yours.

Run the Sum on Your Own Kilometres

Write down three things from the car’s label or its Green Vehicle Guide page: the fuel figure, the electric range and the Test Cycle. If it says NEDC, multiply the fuel figure by the range plus 25, divide by 25, and you have the battery-flat estimate. Then guess the share of your weekly kilometres you can honestly cover from a charge, take that share from 100 per cent, and multiply, and you’ll have a number built on your driving instead of a 25 km average written into a test. Set it against the plain hybrid’s label and the comparison is about you.

Sources: Vehicle Standard (Australian Design Rule 81/02 Fuel Consumption Labelling for Light Vehicles) 2008, Compilation 8, 20 November 2025, clauses (https://www.legislation.gov.au/F2008L00649/2025-11-20/2025-11-20/text/original/epub/OEBPS/document_1/document_1.html); Vehicle Standard (ADR 81/02) 2008, Compilation 8, Appendix C, UN Regulation 101 Annex 8 (https://www.legislation.gov.au/F2008L00649/2025-11-20/2025-11-20/text/original/epub/OEBPS/document_4/document_4.html); Vehicle Standard (Australian Design Rule 81/03 Energy Consumption Labelling for Light Vehicles) 2025, as made 20 November 2025 (https://www.legislation.gov.au/F2025L01402/asmade/2025-11-20/text/original/epub/OEBPS/document_1/document_1.html); Green Vehicle Guide, Fuel consumption label, as published in June 2026 (https://www.greenvehicleguide.gov.au/pages/ToolsAndCalculators/FuelConsumptionLabel); Fraunhofer ISI and ICCT, plug-in hybrid fuel consumption study, press release 9 June 2022 (https://isi.fraunhofer.de/en/presse/2022/presseinfo-16-Kraftstoffverbrauch-Plug-in-Hybridfahrzeuge.html)