This is the methodology we have used to power our calculator which estimates lifecycle CO₂e emissions and total cost of ownership for New Zealand vehicles, including every formula, factor and data source used.

1. Overview

The Opportune NZ Vehicle Emissions Calculator estimates the lifecycle greenhouse gas (GHG) emissions and total cost of ownership (TCO) of a vehicle over a chosen ownership period. "Lifecycle" means the result combines three stages: vehicle manufacturing (embodied emissions), day-to-day use (fuel or electricity burned while driving), and maintenance over the ownership period.

The calculator supports five powertrain types: Petrol, Diesel, Hybrid (HEV, non-plug-in), Plug-in Hybrid (PHEV) and Battery Electric (BEV) and can model a single vehicle or two vehicles side by side for comparison. Every emission factor and default price is shown to the user. The default prices can be overridden, so results stay transparent and auditable rather than being a "black box."

2. The six-step method

Every result the calculator produces is built the same way, in six steps:

1. Identify powertrain & fuel type. Petrol, diesel, HEV, PHEV or BEV, each uses different emission factors, energy inputs and road user charge (RUC) rates.
2. Calculate use-phase emissions. Annual km ÷ 100 × consumption × emission factor, using the applicable fuel or electricity factor.
3. Calculate use-phase energy cost. 2026 fuel prices are entered by grade (regular petrol, premium petrol or diesel); electricity is pre-filled at the 2026 default and remains editable. Price assumptions affect TCO only, never emissions.
4. Add manufacturing emissions. A base, non-battery manufacturing figure by powertrain, plus a battery term (kWh × chemistry factor) for any vehicle carrying a pack.
5. Add maintenance emissions. A per-kilometre maintenance intensity by powertrain, accumulated over the ownership horizon.
6. Sum and scale the lifecycle result. Manufacturing + use phase + maintenance = lifecycle CO₂e. The per-vehicle result can then be multiplied across a selected fleet size.

3. Use-phase emissions

Use-phase emissions are the CO₂e released from burning fuel or drawing electricity while the vehicle is driven. The formula depends on the powertrain:

Battery electric (BEV)

Petrol hybrid (non-plug-in)

Diesel

Plug-in hybrid (PHEV)

These annual use-phase emissions are then multiplied by the number of ownership years to give the use-phase contribution to the lifecycle total.

Tailpipe & electricity emission factors

Table 1: Emission factors applied to energy consumed during the use phase.

4. Use-phase energy cost

Energy prices affect total cost of ownership only. They have no effect on the emissions calculation. Each vehicle carries its own editable price so comparisons can reflect different tariffs or fuel grades.

Table 2: Default 2026 energy prices. Users can overwrite any price with their own tariff or the latest MBIE monitored figure.

Road user charges (RUC)

Diesel and electric vehicles pay road user charges in New Zealand instead of (or in addition to) fuel excise. RUC is charged per 1,000 km travelled and is added to the annual energy cost, but is reported separately in the results and TCO breakdown.

Table 3: Road user charge rates by powertrain (NZTA).

5. Manufacturing (embodied) emissions

Embodied emissions represent the CO₂e released in producing the vehicle before it is ever driven: raw materials, assembly and, for electrified vehicles, battery cell production. This is a one-off figure applied once per vehicle, independent of ownership length.

The battery term applies to any vehicle that carries a pack, BEV, PHEV, and any Hybrid where a battery capacity has been specified. Where no capacity is entered, BEVs default to a 60 kWh pack and PHEVs to a 15 kWh pack; non-plug-in Hybrids default to 0 kWh (no battery term) unless a capacity is explicitly entered, avoiding an inflated result for a conventional hybrid.

Table 4: Base (non-battery) vehicle manufacturing emissions by powertrain (ICCT Life-cycle GHG report, 2025).

Table 5: Battery manufacturing intensity by chemistry (ICCT Life-cycle GHG report, 2025). LFP is the calculator default.

6. Maintenance emissions

Maintenance emissions cover servicing, parts replacement (brakes, fluids, filters, tyres) and associated embodied carbon over the ownership period, scaled by distance travelled.

Table 6: Maintenance emission intensity by powertrain (ICCT, 2025). Electrified powertrains carry lower rates, reflecting fewer moving parts and no engine-oil servicing.

7. Lifecycle total & total cost of ownership

Lifecycle emissions

End-of-life emissions (recycling, disposal) are not modelled as a separate stage in this version and is currently not included in our calculator.

Total cost of ownership (TCO)

For fleet scenarios, the per-vehicle lifecycle emissions and TCO are simply multiplied by the number of vehicles in the fleet.

8. Worked example: comparing all five powertrains

The table below applies the exact formulas above to a common New Zealand scenario: 15,000 km driven per year over a 5-year ownership period, using each powertrain's default consumption figure, regular-grade petrol where applicable, LFP battery chemistry, and 2026 default energy prices. No purchase price is included, so the cost column reflects energy and RUC only.

Table 7: Illustrative comparison at 15,000 km/yr over 5 years using calculator defaults. Figures are rounded to two decimal places; small rounding differences versus a live calculation are expected. BEV and PHEV manufacturing includes a default battery pack (60 kWh and 15 kWh respectively) at the LFP factor.

This example illustrates a consistent pattern across New Zealand's electricity mix: electrified powertrains carry higher manufacturing emissions (largely from the battery) but substantially lower use-phase emissions, so the lifecycle total falls as electrification increases, even before any grid decarbonisation is factored in. The crossover point depends heavily on annual distance and ownership length, which is why the calculator lets users adjust both.

9. Data sources

Table 8: Full source list. All factors mirror Opportune's internal GHG spreadsheet model to keep the calculator and master workbook aligned.

10. Assumptions & limitations

• Energy prices are editable defaults, not live feeds. Users should check the linked MBIE pages for the latest monitored price before relying on TCO figures for a decision.
• Emission factors reflect New Zealand-specific fuel and grid data and are not directly transferable to other countries.
• Results are estimates intended to support decision-making and reporting; they are not a substitute for a vehicle-specific life-cycle assessment or an audited emissions inventory.