Start with a matched purchase difference
Obtain dated gasoline and iDD quotations for vehicles that meet the same passenger and destination requirements. Separate condition, fitted equipment, preparation and delivery scope before calling the gap a powertrain premium. The gasoline versus iDD guide remains the broader choice; this calculation addresses whether the extra prepared expenditure can be justified financially. If the iDD includes useful equipment missing from the gasoline offer, record that value separately instead of attributing every price difference to energy savings. Conversely, an unexplained lower-priced gasoline vehicle is not a valid baseline until its consequential inspection and support questions have been addressed.
Use charging days that you can actually secure
Write an ordinary week with journeys, parking windows and reliable charging locations. Distinguish charging you control from a public point that may be unavailable or occupied. Use the home installation review when property access is part of the proposal. Include a week without that access and seasonal changes rather than assuming the entire annual distance is electric. Installation cost and any fixed charging fees belong in the premium or operating worksheet, not outside the comparison. A supplier’s quoted charger output does not establish how much useful energy your exact car will accept during the time available.
Measure costs at the boundary where you pay
For the electric portion, use purchased electricity and the actual tariff, including relevant session or parking charges, rather than battery energy alone. Keep the gasoline portion visible because the iDD remains a plug-in hybrid. Compare actual or clearly labelled planning consumption under the same route, load and climate assumptions; brochure figures from different cycles do not make matched operating costs. The range and energy guide explains that measurement boundary. Separate engine care and charging costs from traction energy. Do not claim a universal number of kilometres needed to recover the premium when prices, access and daily use differ between buyers.
Calculate an annual saving and a conditional break-even
Define annual energy saving as the matched gasoline expenditure minus the combined iDD electricity and fuel expenditure. Subtract any incremental recurring expense you can identify; do not assume that every maintenance item cancels out. Divide the accepted prepared premium, including necessary charging setup, by a positive net annual saving to obtain a simple payback estimate. If the result is zero or negative, this worksheet does not produce an energy-cost payback. Keep the units and time period consistent. The three-year ownership worksheet adds wider spending and resale assumptions; simple break-even alone is not total ownership value or a forecast of reliability.
Test the decision with worse but plausible use
Run a second case with fewer charging days, higher purchased energy cost, lower annual distance and any separately quoted support expense. Change one input at a time so the reason for a different result stays understandable. If the favourable case recovers the premium only beyond your planned ownership period, do not present it as near-term savings. Confirm usable destination support through the maintenance and parts plan. Keep repair contingencies labelled rather than creating an invented fixed battery allowance. A higher-priced iDD can still have non-financial appeal, but comfort or driving preference should not be disguised as proven fuel-cost recovery.
Record what would invalidate the premium argument
Keep both offers, the installation scope, tariff evidence, annual-distance estimate, charging availability and calculation date together. Identify the inputs you must refresh if the VIN, home, route or ownership period changes. A replaced iDD candidate needs renewed battery and charging review; it cannot inherit the first vehicle’s acceptance. For a buyer relying entirely on public access, use the no-home-charging purchase decision before commitment. The final choice should say whether the premium is financially supported, justified by another explicitly valued benefit, or still conditional. It should remain intelligible without a guaranteed resale premium or a seller’s optimistic electric-driving percentage.
Compare the acceptance conditions
- Positive case
- A matched premium and credible charging schedule produce useful net savings within the planned holding period.
- Preference-led
- Accept the extra cost for a stated non-financial benefit without claiming energy payback.
- Unresolved
- Do not commit on a savings claim while charging access or matched costs remain unknown.
Buyer evidence checklist
- Match the offers and preparation.
- Include complete charging setup.
- Keep paid electricity and gasoline separate.
- Calculate net annual saving with consistent units.
- Test reduced charging and a shorter holding period.
Questions before you buy
Is the brochure electric range enough to calculate payback?
No. Actual charging access, purchased energy, route use and the prepared premium are necessary inputs.
What if estimated annual savings are negative?
The simple worksheet does not demonstrate an energy-cost payback. Consider other explicitly valued benefits or a different offer.