For a plug-in hybrid, a single combined economy figure can hide two expensive questions: how often will the car be charged, and how much petrol will be used after the battery is depleted? A useful calculation for a 2020–2026 PHEV deliberately separates those modes.
Track electric and combustion kilometres
Start with actual weekly travel and estimate the share of kilometres that can be completed using grid electricity under realistic conditions. Use vehicle-specific energy consumption and charge-sustaining fuel consumption in the correct market test system. Do not assume the advertised electric range will be repeated in winter or that the engine will never engage during a short trip.
Build two lines of energy expense
Electric expense is energy drawn from the grid multiplied by the applicable tariff; add a measured or clearly labelled allowance for charging losses if the consumption figure is battery-side. Petrol expense is fuel consumed in engine-running driving multiplied by pump price. A public charging tariff can differ sharply from a household tariff. Separate those bills rather than converting kWh to an invented universal petrol equivalent.
Challenge the optimistic scenario
Calculate a favorable case with regular home charging, an expected case and an inconvenient case with little charging. The European Commission found that PHEV real-world emissions in a 2021 registered fleet were materially higher than laboratory WLTP results, partly because actual charging was less frequent than expected. The study does not prove the outcome for any one model or owner.
An illustrative formula is not a promised bill
For a journey with separate electric and petrol segments, calculate each segment from its own relevant consumption unit and purchased-energy price. Keep charging losses visible as an assumption unless the official metric is measured at the plug. For a blended-use vehicle that starts the engine even when charge remains, use manufacturer or independently established operational data instead of assuming every first kilometre is electrically driven.
Who should choose it?
Only claim that a PHEV saves money once the scenario includes the additional purchase cost, maintenance needs and expected ownership period. If regular charging cannot be assured, the favorable case is not the right headline.
Model-year and market scope
Applies to 2020–2026 PHEVs. No local prices, electric-mode share or battery losses are inserted without buyer-specific inputs.