How to calculate the cost of charging your EV

The cost of any single charging session is just: kWh added × price per kWh = total cost. Everything else is figuring out the two numbers on the left.

kWh added is the difference between your starting and ending battery state expressed in kWh, not percent. For a 60 kWh usable battery going 20% to 80%, that's 60 × (0.80 - 0.20) = 36 kWh. Multiply by the price (say £0.77/kWh on a UK motorway rapid) and the session costs 36 × £0.77 = £27.72.

Manufacturers usually quote two numbers — gross (total cells installed) and usable (the bit you can actually access). For cost maths, always use usable. Typical values: Tesla Model 3 LR 75 kWh usable; Hyundai Ioniq 5 77 kWh; Kia EV6 GT-Line 77 kWh; BYD Atto 3 60 kWh; MG4 Extended Range 74 kWh; Renault Megane E-Tech 60 kWh.

Our vehicle database lists usable battery for every model we track. If in doubt, the figure on a manufacturer's spec sheet labelled 'usable' or 'net' is the one you want.

Once you know your usable battery, percent → kWh is one multiplication. A Hyundai Ioniq 5 going from 25% to 78% adds (0.78 - 0.25) × 77 = 40.8 kWh. Quick mental shortcut: 1% on a 77 kWh battery is about 0.77 kWh; on a 60 kWh battery it's 0.6 kWh.

Be aware that the in-car battery percentage and the percentage the charger reports are sometimes 1-3% apart due to rounding and BMS hysteresis. For cost estimation that doesn't matter; for an exact bill, trust the session receipt.

Use the price you'll actually pay — your subscription rate if you have one, the ad-hoc rate if not. Common 2026 reference prices: UK home off-peak £0.08, UK motorway rapid £0.77, French Heures Creuses €0.18, French Ionity ad-hoc €0.59, Italian F2/F3 €0.25, Italian Ionity ad-hoc €0.59, Australian off-peak EV AU$0.12, Australian Evie ad-hoc AU$0.67.

Worked example: charging a Kia EV6 from 18% to 80% on a UK Ionity rapid at £0.69/kWh subscription rate = (0.80 - 0.18) × 77 × £0.69 = 47.7 × £0.69 = £32.93. The same session at the £0.85 ad-hoc rate would be £40.55 — the subscription is worth around £8 per session.

Per-session cost tells you what you spent today; per-100-km cost tells you whether the EV is fundamentally cheap or expensive to run. The formula is: consumption (kWh/100 km) × price/kWh = cost per 100 km.

A Tesla Model 3 at 15 kWh/100km on UK home off-peak: 15 × £0.08 = £1.20 per 100 km. Same car on UK motorway rapid: 15 × £0.77 = £11.55 per 100 km. A petrol Golf at 6.5 L/100km × £1.45 = £9.43 per 100 km. The Model 3 on rapid is roughly the same as a petrol Golf; the Model 3 on home off-peak is roughly 8× cheaper. Use our charging calculator to plug in your own numbers.

Once you've done the calc a few times, most owners switch to a mental shortcut. For a 60 kWh usable battery, every 10% of SoC ≈ 6 kWh. At £0.77/kWh that's roughly £4.60 per 10% on a UK rapid, £0.50 per 10% on home off-peak. For 77 kWh batteries, every 10% ≈ 7.7 kWh — call it £6 per 10% on UK rapid, £0.60 on home.

Plug-and-charge displays and most network apps now show running session cost in real time, so the formula is mainly useful for deciding whether to plug in at all, and for sanity-checking your monthly bill.

Taking the same charging session — a Tesla Model 3 LR (75 kWh usable) going from 60% to 100% — and pricing it across our four markets at common networks shows exactly how location and price tier affect the final bill. The session adds 30 kWh of energy regardless of where you do it; only the per-kWh price changes.

Per-kWh rate isn't always the full bill. Watch for three line items that surprise new drivers. Session/connection fees — Ionity, Allego and some legacy UK networks charge £0.50-£1.50 per session on top of the per-kWh rate. Negligible on a 30-minute rapid stop, meaningful on a 5-minute top-up that doubles the effective rate.

Idle/overstay fees — Tesla, Ionity, Evie and several others charge per-minute fees if you leave the car plugged in after it's full. Tesla's idle fee in the UK is £0.50/min during congestion. Easy to avoid by moving the car promptly. Time-of-day surcharges — Tesla Superchargers in particular use dynamic pricing that varies by site, time and demand; the same stall can be 30% more expensive at 6pm Friday than 2am Wednesday. Always check the live price in the app before plugging in.

Most experienced EV owners eventually stop calculating individual sessions and use a once-a-year shortcut: annual kWh × blended price/kWh = annual fuel cost. Annual kWh = annual km × consumption (kWh/100 km) ÷ 100. Blended price comes from your charging mix — typically 75-85% home off-peak and 15-25% public for most owners.

Example: 12,000 km/year in a Tesla Model 3 LR at 15 kWh/100 km = 1,800 kWh. With 80% home off-peak at £0.08 and 20% rapid at £0.77, blended price is £0.218 — annual fuel £392. Plug your numbers into our charging calculator for an exact answer and to compare against a petrol equivalent.

For trip planning, the question shifts from per-session cost to total trip cost. The formula is the same building blocks: total km × consumption ÷ 100 = total kWh; then split that kWh between home (cheap) and rapid (expensive), and price each portion.

Worked example: 660 km London → Edinburgh in a Hyundai Ioniq 5 at 17 kWh/100 km = 112 kWh total. Leave home with a full battery (cost ~£6 of home off-peak energy in the car already). Use about 50 kWh at home rates (already in the car) and 62 kWh on rapid. At UK Tesla Supercharger non-Tesla rates of £0.59/kWh, that's £36.58 in rapid charges. Total trip fuel: roughly £43, vs £62 in a 6.5 L/100 km Skoda Octavia petrol. The lesson: home-charging the start meaningfully cuts trip cost because the cheapest kWh in the trip are the ones you put in the night before.

Five small errors that quietly distort the cost number. First, using gross battery capacity instead of usable — overstates kWh added by 5-10%. Second, forgetting the small in-cabin systems (heating, sound system, infotainment) that consume 0.5-1 kWh per hour parked-and-charging in cold weather. Third, assuming SoC% on the dash equals SoC% on the charger receipt — they can differ by 1-3% due to BMS hysteresis.

Fourth, ignoring session fees on per-session pricing (Ionity, Allego sometimes add £0.50-£1.50 per session). Fifth, comparing 'what the charger said it added' to 'what the car battery moved' — DC charger meters measure energy delivered to the car including charging losses (typically 3-7%), so charger kWh > car-display kWh added is normal, not a fault.