EV Charging Calculator

Methodology

Every charging curve, time and cost on this site is computed from a proprietary chemistry-up model. Here's exactly how that model works.

The chemistry-up approach

Most EV calculators store per-car charging curves as fixed arrays of data points, copied from third-party tests like Fastned's published curves or independent reviews. We don't do that — there are two problems with it.

First, variant blindness. "Tesla Model Y" isn't one car. A UK-spec Long Range built in Berlin from 2024 onwards has LG NMC 811 cells; the same model name in some other markets has Panasonic NCA or CATL LFP cells. They charge differently. A single stored curve hides that.

Second, fragility. When a manufacturer switches cell suppliers — as Tesla did with the UK Model Y in 2024 — every stored curve based on the old data is wrong until someone manually re-tests. With a chemistry-up model, you just update the chemistry mapping for that variant and every downstream number on the site refreshes on the next build.

How the model works

For each EV in the launch lineup we identify:

From those inputs, a single pure function — deriveChargingCurve — interpolates piecewise-linearly between the C-rate anchors, multiplies by pack-level derating, BMS aggressiveness and ambient-temperature factors, and produces a 0–100% SOC curve in kW. The function runs in under a millisecond per car, so it can re-derive curves live in the browser when you change the ambient temperature slider.

Calibration

For every car in the launch lineup, the model's derived peak DC sits within 10% of the publicly verifiable peak that the manufacturer or independent road tests have measured. This is enforced by the test suite: if a calibration drifts on a future data update, the build fails before deploy.

Calibration is editorial work — picking pack-level parameters that produce sensible results across the chemistry's full set of cars. When two different cars share the same cell chemistry (e.g. the Hyundai Ioniq 5 and the Kia EV6 both use SK On NMC pouch cells on the E-GMP platform), the difference between their curves is captured by their pack-level derating, BMS calibration and pre-conditioning settings — never by silently rewriting the cell-level numbers.

Sources for the cell-level parameters

Each cell chemistry entry on the site links to its manufacturer's publicly published cell datasheet or product page. We use those — plus academic battery testing literature, manufacturer technical announcements, and our own back-calculation from publicly known peak DC — to set the C-rate anchor values for each chemistry. The numerical C-rates themselves are physics facts, not copyrightable, and the parameters we choose are calibrated independently against verifiable peaks.

We don't copy charging curve points from EV Database, Fastned, Carwow road tests or any other third-party paid or proprietary source. The model is fully our own.

Charging time, AC vs DC

For DC fast charging, the delivered power at each SOC step is the minimum of the charger's maximum kW and the car's accepted kW per the derived curve. Above 80% SOC the curve tapers steeply for most chemistries, which is why most rapid sessions end there.

For AC charging (7kW or 22kW units), the limit is the vehicle's onboard AC charger, not its DC peak. A 22kW destination charger paired with an 11kW onboard charger delivers 11kW, not 22. The DC charging curve is ignored — it's a different physical pathway through the car.

Charging cost

Cost is delivered kWh × rate, plus any session fee, with the result raised to the minimum charge floor if one applies. Subscription tariffs report the per-session cost; the monthly fee is shown separately so you can decide whether the volume justifies it.

All prices are VAT-inclusive at the rate the network publishes. A February 2026 First-tier Tribunal ruling could move public charging from 20% to 5% VAT; we'll update each network as it implements that change.

Cost per mile

We use real-world Wh/mile figures derived from independent road tests rather than WLTP. WLTP is optimistic for most cars and significantly so for high-power EVs at motorway speeds. Real-world range on each per-car page is the same Wh/mile figure run the other way — usable kWh divided by Wh/mile — so the range and the cost-per-mile values always reconcile.

Multi-car comparison

The comparison tool overlays up to three EVs against the same shared inputs. It calls the same time and cost engines described above, once per car, with identical charger speed, SOC range and ambient temperature. The chart's curve view shows each car's derived kW at every SOC; the time-elapsed view shows delivered kW across the actual session; the cumulative-SOC view shows how SOC climbs over time. No new maths is introduced by the comparison — it's a composition layer over the single-car calculators, so any update to the chemistry model flows through to every comparison page on the next build.

Tariff calculator

The tariff calculator ranks UK domestic electricity tariffs by how much they would cost your household each month — given your car, your mileage, your home charger, and your non-EV electricity usage. It models seven tariffs at launch: the Ofgem standard variable price cap (as the baseline), Octopus Go, Intelligent Octopus Go, OVO Charge Anytime, EDF GoElectric Overnight, British Gas Electric Driver, and E.ON Next Drive.

Three components per tariff make up the monthly total: EV charging cost, non-EV household cost, and the standing charge. We use 365.25 ÷ 12 = 30.4375 as the days-per-month constant.

EV charging cost

Monthly EV kWh is derived from the car's real-world Wh/mile efficiency (from our chemistry-up model) multiplied by monthly miles. We then apply an off-peak share factor based on how much of your charging you can actually time-shift:

These four presets are deliberately coarse. They're calibrated to be roughly correct for a representative UK household; the methodology page lists them so a more careful user can pick the bucket that fits them or use the bookmarkable URL to share a specific scenario.

Non-EV household cost

Non-EV electricity usage (the rest of the home — heating, cooking, lighting, appliances) is split 75% peak / 25% off-peak by default. The reasoning: most off-peak windows are 5-7 hours overnight, which is ~22-29% of the day. Some appliances (storage heating, dishwashers, washing machines) shift naturally into those hours; most do not. 25% is a reasonable model assumption — slightly optimistic for a household that doesn't deliberately time-shift, slightly pessimistic for one that does.

If you know your own home's split better than this default, the model exposes its assumption openly so you can adjust expectations. The bigger the gap between peak and off-peak rates, the more this assumption matters for the verdict.

OVO Charge Anytime's EV-only off-peak

OVO Charge Anytime is modelled with its quirk: the 7p/kWh rate applies only to EV charging, identified by smart-charger telemetry. The rest of the home stays on the standard peak rate. Our model handles this with an evChargingOnlyOffPeak flag on the tariff — when set, the off-peak rate is applied to EV kWh at 100% share and the non-EV split is bypassed. This is why OVO Charge Anytime appears differently in the ranking depending on your non-EV usage: it benefits EV-heavy, non-EV-light households more than the other way round.

Off-peak achievability check

A tariff that gives you 7p/kWh for 5 hours a night only saves money if you can actually deliver enough kWh into the car in 5 hours a night. For a 3kW granny lead that's at most ~15 kWh per night, or ~456 kWh/month — well below what a 2,000-mile-per-month driver needs.

We compute the maximum deliverable off-peak kWh as charger kW × off-peak hours/day × 30.4375. If your declared off-peak share would require more than that, the achievability indicator flips amber/red and we surface the gap. The cost ranking still uses your declared share — we don't second-guess your inputs — but you see exactly when the model is being unrealistic about a particular charger.

What the tariff calculator doesn't model

Tariff rates change frequently — quarterly at minimum, sometimes mid-cycle. Every tariff in the dataset has a lastVerified date and a link to the provider's published rate card. Verify on the provider's site before switching.

Tariff data and verification

Every network entry cites the URL of its published tariff page and a last-verified date. We comprehensively review tariffs quarterly and have an automated weekly check that flags any tariff page that has changed since last verification, triggering a manual update.

What we don't do

We don't scrape live tariffs. We don't republish ZapMap data. We don't recommend networks based on affiliate rate — affiliates are clearly disclosed but never influence rankings. We don't claim our chemistry-up model is a perfect simulation of every real-world charging session — it's an honest, transparent approximation calibrated against publicly verifiable peaks, which is better than the "naive peak with linear taper" calculators that dominate the alternatives.

Intellectual property

The chemistry model — the algorithm, the cell-level C-rate parameters per chemistry, the car-to-chemistry mapping, and the calibration approach — is our proprietary work. See the Terms of Use for what's allowed and what isn't.