Plug-in Hybrid Economy Calculator (PHEV running cost)

Understanding the plug-in hybrid cost calculator — concept and principle

This calculator estimates the yearly energy cost and tailpipe CO₂ of a plug-in hybrid (PHEV), split between electric driving and hybrid driving, and compares it with a petrol car covering the same distance. Use it when deciding whether a PHEV suits your driving and charging habits.

Electric km plus fuel km: with the default inputs the result is $1,011 a year (saves $901.50 vs petrol).

How it is calculated

Electric km = yearly km × electric share; fuel km = the rest.
Grid electricity (kWh) = electric km × kWh/100 km ÷ 100 ÷ (1 − charging losses).
Fuel (L) = fuel km × L/100 km ÷ 100.
Cost = kWh × electricity price + litres × fuel price; per 100 km = cost ÷ km × 100.
Petrol car cost = km × its L/100 km ÷ 100 × fuel price.
Tailpipe CO₂ = litres × 8.887 ÷ 3.785 kg (US EPA, 2.35 kg per litre of petrol).

The principle

A plug-in hybrid runs on battery power for shorter trips and switches to its petrol engine when the battery is empty, so its costs depend heavily on how often you charge. Charging loses some energy as heat in the charger and battery, so more electricity is drawn from the grid than reaches the wheels. The tailpipe of a PHEV emits nothing in electric mode, which is why its CO₂ is far below a comparable petrol car when the electric share is high; the electricity's own emissions depend on your grid.

Worked example

Default inputs: 15,000 km a year, 60% electric, 18 kWh/100 km, 10% charging losses, $0.25/kWh, 5.5 L/100 km in hybrid mode, $1.70/L, comparable petrol car 7.5 L/100 km.

Electric km = 9,000; fuel km = 6,000.
Electricity = 9,000 × 18 ÷ 100 ÷ 0.9 = 1,800 kWh = $450.00.
Fuel = 6,000 × 5.5 ÷ 100 = 330 L = $561.00.
Total = $1,011.00 a year, or $6.74 per 100 km.
Petrol car = 1,125 L × 1.70 = $1,912.50; saving $901.50. Tailpipe CO₂: 775 kg versus 2,641 kg.

Each point is the calculator re-run with only “Distance driven per year (km)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Distance driven per year (km)	Yearly energy cost
3,750	$252.75
7,500	$505.50
11,250	$758.25
15,000	$1,011.00
18,750	$1,263.75
22,500	$1,516.50
30,000	$2,022.00

How to read the result

The electric share is the biggest lever. A PHEV that is rarely charged can cost as much as, or more than, a normal hybrid because it carries a heavy battery. Measure your real electric share from the car's trip data after a few months and re-run the calculation. Compare with a full hybrid or battery electric car too.

Common mistakes

Using the official electric range, which is often higher than real-world range.
Forgetting charging losses.
Using a cheap night tariff for all charging when some happens at public chargers.
Counting electric driving as zero emissions overall.

Keep in mind: Tariffs, fuel prices and real consumption vary. This is an estimate, not financial advice.

Frequently asked questions

How much does a plug-in hybrid cost to run?

In the example, about $1,011 a year for 15,000 km with 60% electric driving.

What happens if I never charge a PHEV?

It runs as a hybrid on petrol, losing most of the savings.

How much CO₂ does a litre of petrol produce?

About 2.35 kg at the tailpipe, using the US EPA figure.

Sources: US EPA, "Greenhouse Gas Emissions from a Typical Passenger Vehicle" · NIST Special Publication 811 (2008), Appendix B (1 US gallon = 3.785411784 L)

Checked 9 Nov 2026. Energy-cost arithmetic; tailpipe CO₂ from US EPA, “Greenhouse Gas Emissions from a Typical Passenger Vehicle” (8,887 g CO₂ per gallon of gasoline); 1 US gallon = 3.785411784 L (NIST SP 811). Use your car’s measured consumption and your own tariff for the inputs.

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