Why doesn't my bill match the calculator?

I use regional averages and published MSRP-class prices. Your tariff, discounts, on-road costs, and driving pattern will differ — use overrides where helpful.

Is the EV or petrol 'winner' guaranteed?

No. TCO is sensitive to km driven, energy prices, and how long you keep the car. The result is a structured estimate, not a recommendation.

How often are vehicle prices updated?

I flag prices for review when my source checks are older than the freshness window (about 45 days). The 'last updated' field on results reflects data refresh, not real-time dealer quotes.

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Methodology

How CarCostIQ computes total cost of ownership (TCO) for EVs vs petrol cars in Australia.

Reference v1.1

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1. TCO Formula

Total cost of ownership over the chosen period (default 5 years) is:

TCO = Purchase cost
    + Energy cost (electricity or fuel over period)
    + Insurance (annual × period years)
    + Maintenance (annual × period years)
    + Loan interest (if applicable)
    − Residual value (at end of period)

All values in AUD. Energy cost uses annual km, efficiency (kWh/100km or L/100km), and regional energy prices.

2. Assumptions Explained

Annual km: Distance driven per year. Used to compute energy cost.
Electricity (c/kWh): Home/meter price per kWh. Defaults by state/territory. The charging mix blends this home rate with an independent public DC fast-charging rate (its own c/kWh value, default ~55 c/kWh, editable in Advanced) for the share you don't charge at home. The mix defaults to 80% home charging — real-world Australian EV owners do most, but not all, of their charging at home; the remaining share is priced at the regional public rate:effective = home·(1−offPeak)·home% + public·(1−home%)This replaces the earlier model that estimated public charging as a fixed multiple of the home rate (see changelog). The optional home off-peak / solar discount reduces only the home-charged portion — a rough proxy, not a tariff model.
Fuel (c/L): Petrol price per litre. Defaults by region.
Insurance (annual): Flat annual estimate. Defaults: EV ~$1,200, Petrol ~$1,000.
Maintenance (annual): Flat annual estimate. Defaults: EV ~$400, Petrol ~$800.
Residual rate: Fraction of purchase price retained at end of period. Base defaults are per powertrain: EV 45%, Petrol 50%, Hybrid 55%, Diesel 58%, PHEV 45% — reflecting Australian resale patterns (utes and Toyota-style hybrids hold value better than mainstream petrol; plug-in hybrid used demand is softer, so it tracks the EV rate). The base default then tapers with mileage: above a normal allowance of 15,000 km/year, the rate is reduced by 4% (relative) per extra 10,000 lifetime km, with a hard floor of 12%. So a high-km car is credited a lower resale value than a low-km one. An explicit residual you enter is used as-is (no taper, no floor). The same taper applies across powertrains; EVs may depreciate faster at very high km (battery wear), so an EV-specific taper is a likely future refinement.
Period years: Comparison horizon (default 5 years).

3. OEM-First Vehicle Price Policy (Australia)

Vehicle prices (MSRP) follow a strict source hierarchy:

Official OEM Australia website pages (Build & Price / Model pages)
Australian government sources
Public data sources
Media references (fallback only)
Manual entries (temporary only, marked for review)

Approved OEM Australia sources:

Government cross-check:

Green Vehicle Guide

Efficiency & energy figures (kWh/100km, L/100km) do not follow the price hierarchy above. They come from official ADR 81/02 test data (Australian Government), published via the Green Vehicle Guide.

MSRP limitations: Prices exclude on-road costs (stamp duty, registration) unless noted. Regional dealer variations may apply.

Freshness: When I have not re-checked an MSRP source for longer than my usual window (about 45 days), I flag that vehicle price for review before the next data refresh. This keeps listings honest without pretending quotes are real-time dealer prices.

Regional prices — Electricity and fuel by state/territory. Updated periodically.

4. Major methodology updates

v1.2 — Public DC fast-charging is now an independent rate (default ~55 c/kWh, editable) instead of a fixed multiple of the home rate. Residual value tapers with mileage above 15,000 km/year (floored at 12%), so high-km cars are credited less resale value; an explicit residual override is used as-is. Diesel vehicles now use the region's diesel price rather than falling back to petrol.
v1.1 — Added methodology version marker; expanded transparency on OEM-first pricing and price freshness checks.
v1.0 — Initial public methodology: 5-year TCO formula, regional energy defaults, flat insurance/maintenance assumptions, residual as fraction of MSRP.

5. FAQ (practical)

Why doesn't my bill match the calculator?: I use regional averages and published MSRP-class prices. Your tariff, discounts, on-road costs, and driving pattern will differ — use overrides where helpful.
Is the EV or petrol "winner" guaranteed?: No. TCO is sensitive to km driven, energy prices, and how long you keep the car. The result is a structured estimate, not a recommendation.
How often are vehicle prices updated?: I flag prices for review when my source checks are older than the freshness window described above. The "last updated" field on results reflects data refresh, not real-time dealer quotes.

6. Limitations & Disclaimer

Estimates only. Actual costs vary with driving style, location, and market conditions.
Insurance and maintenance use flat annual assumptions; real costs may differ.
Residual values are estimates; resale markets fluctuate.
Energy prices are regional averages; home solar, off-peak tariffs, or fuel discounts not modelled.
Not financial or investment advice. Use for comparison only.

Try it yourself

Every assumption above is editable in the calculator — run your own comparison with your state, annual km and vehicles.

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