Why does the PHEV cost depend on the number of charges rather than just mileage?

The calculator assumes each charge fills the battery to the stated capacity and delivers a fixed electric range. Multiplying charges per year by electric miles per charge gives total EV miles; the remainder uses petrol. This models real-world charging habits more accurately than assuming optimal charge timing.

What happens if I set PHEV charges to zero?

The PHEV will behave as a conventional hybrid, running entirely on petrol at the stated ICE-mode MPG. The electric-cost component becomes zero, and the result will reflect pure petrol consumption.

Does the tool account for off-peak electricity tariffs?

Only if you enter the blended or effective rate you pay per kWh. The calculator multiplies total kWh consumed by the single electricity price provided; if you charge overnight at a lower rate, calculate your average cost per kWh first.

Why might the hybrid cost less than the PHEV despite lower MPG?

If the PHEV is charged infrequently, most miles run on petrol at the PHEV's ICE-mode MPG, which is often lower than a dedicated hybrid's combined MPG. Additionally, electricity cost for even a small number of charges adds to the total, potentially exceeding the hybrid's all-petrol cost.

Can I use this tool to compare different vehicle models?

Yes, by entering each model's published efficiency figures and your expected charging behavior. The calculator shows which powertrain type yields the lowest running cost for your specific mileage and energy prices, but does not include purchase price, depreciation, or other ownership costs.

EV vs ICE

Hybrid vs PHEV vs Pure EV

Compare annual fuel costs across hybrid, plug-in hybrid (PHEV) and pure EV powertrains.

Last updated: 18 May 2026

What this tool does

This calculator compares the annual fuel and electricity costs of three powertrain types: conventional hybrid, plug-in hybrid (PHEV), and battery electric vehicle (EV). It requires your annual mileage, the hybrid's combined MPG, the PHEV's electric range per charge and number of charges per year, the EV's efficiency in miles per kWh, and current fuel and electricity prices. The tool outputs the lowest annual cost among the three powertrains and displays the breakdown for each. Results assume the stated efficiency figures are accurate and that charging behavior remains consistent throughout the year.

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Formula

C_{annual} = min (\frac{4.546 \times P _{fuel}}{M _{h}} \times D, (N_{c} \times B_{kWh} \times P_{elec}) + \frac{4.546 \times P _{fuel}}{M _{ice}} \times max (D - min (R_{c} \times N_{c}, D), 0), \frac{P _{elec}}{E _{ev}} \times D)

C_{annual}

Minimum annual fuel/energy cost (£)

D

Annual miles driven (mi)

M_{h}

Hybrid fuel efficiency (MPG)

M_{ice}

PHEV ICE fuel efficiency (MPG)

P_{fuel}

Petrol price per litre (£/L)

P_{elec}

Electricity price per kWh (£/kWh)

How Hybrid vs PHEV vs Pure EV works

The calculator computes three separate annual running costs. For the conventional hybrid, it divides your annual mileage by the stated MPG, converts gallons to liters using the imperial gallon factor 4.54609, then multiplies by the petrol price per liter. For the PHEV, it first calculates electric miles as the product of charges per year and EV range per charge (capped at total annual mileage), then subtracts that from total mileage to find petrol miles; electric cost is the number of charges multiplied by battery size in kWh and electricity price, while petrol cost uses the remaining miles divided by the PHEV's ICE-mode MPG. For the pure EV, annual mileage is divided by efficiency in miles per kWh, then multiplied by the electricity price. The tool identifies which powertrain produces the lowest annual cost.

The formula

Hybrid: Annual cost = (miles_per_year ÷ hybrid_mpg) × 4.54609 × petrol_price_per_liter
PHEV: EV_miles = min(phev_ev_miles_per_charge × phev_charges_per_year, miles_per_year); ICE_miles = miles_per_year − EV_miles; Annual cost = (phev_charges_per_year × phev_battery_kwh × elec_price_per_kwh) + (ICE_miles ÷ phev_ice_mpg × 4.54609 × petrol_price_per_liter)
EV: Annual cost = (miles_per_year ÷ ev_miles_per_kwh) × elec_price_per_kwh

Where this method is most accurate

Results reflect real-world costs when the input efficiency figures match actual driving conditions. Hybrid and PHEV MPG can vary significantly with highway versus city driving, ambient temperature, and accessory use. PHEV calculations assume the stated number of charges per year is achieved; irregular charging will shift more miles to petrol mode. EV efficiency depends on speed, climate control, and terrain. Electricity and petrol prices should represent the rates actually paid, including off-peak tariffs for home charging if applicable. The tool does not model seasonal variation, battery degradation, or maintenance costs.

What this tool does not do

The calculator does not include purchase price, depreciation, road tax, insurance, servicing, or tire replacement. It does not estimate emissions, home-charger installation cost, or public charging network availability. The tool cannot determine which powertrain best suits a particular journey profile; it only compares annual energy costs using the inputs provided. It does not verify whether a given PHEV battery size or EV range is achievable in practice, nor does it account for regenerative braking differences or real-time tariff switching.

Disclaimer

This calculator is an educational tool that performs arithmetic on user-supplied figures. It does not constitute vehicle purchase advice, financial advice, or a guarantee of actual running costs. Real-world efficiency varies with driving style, weather, vehicle condition, and route type. Users remain responsible for verifying manufacturer specifications and obtaining independent professional advice before making vehicle or financial decisions.

Questions

Why does the PHEV cost depend on the number of charges rather than just mileage?: The calculator assumes each charge fills the battery to the stated capacity and delivers a fixed electric range. Multiplying charges per year by electric miles per charge gives total EV miles; the remainder uses petrol. This models real-world charging habits more accurately than assuming optimal charge timing.
What happens if I set PHEV charges to zero?: The PHEV will behave as a conventional hybrid, running entirely on petrol at the stated ICE-mode MPG. The electric-cost component becomes zero, and the result will reflect pure petrol consumption.
Does the tool account for off-peak electricity tariffs?: Only if you enter the blended or effective rate you pay per kWh. The calculator multiplies total kWh consumed by the single electricity price provided; if you charge overnight at a lower rate, calculate your average cost per kWh first.
Why might the hybrid cost less than the PHEV despite lower MPG?: If the PHEV is charged infrequently, most miles run on petrol at the PHEV's ICE-mode MPG, which is often lower than a dedicated hybrid's combined MPG. Additionally, electricity cost for even a small number of charges adds to the total, potentially exceeding the hybrid's all-petrol cost.
Can I use this tool to compare different vehicle models?: Yes, by entering each model's published efficiency figures and your expected charging behavior. The calculator shows which powertrain type yields the lowest running cost for your specific mileage and energy prices, but does not include purchase price, depreciation, or other ownership costs.

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Sources & Methodology

The hybrid cost uses (annual_miles ÷ MPG) × 4.54609 L/gal × petrol_price to convert imperial MPG to liters of petrol. PHEV cost sums electricity for the stated number of full charges (charges × battery_kWh × elec_price) and petrol for remaining miles. EV cost is (annual_miles ÷ mi_per_kWh) × elec_price. The imperial gallon constant 4.54609 is used for standard MPG-to-liter conversions.

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Hybrid vs PHEV vs Pure EV

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How Hybrid vs PHEV vs Pure EV works

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Where this method is most accurate

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Questions

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