How we compare

The sum

For each tariff we estimate a year of electricity:

Car electricity (kWh) = miles per year ÷ miles per kWh

Yearly cost = standing charge × 365
            + car electricity at the cheap rate (if the tariff allows it)
            + home use, split between the day rate and the cheap rate

The monthly figure is the yearly cost divided by 12. Pence per mile is the cost of charging your car divided by your miles.

Assumptions

• All car charging happens at home, during the cheap hours, when the tariff allows it. If you also use public chargers, your home cost will be lower.
• Defaults if you're not sure: 3.5 miles per kWh, 7,400 miles a year (UK average), and 2,700 kWh a year of home use (Ofgem's typical figure).
• Moving home use overnight: "None" puts 0% of your home use in the cheap hours, "Some" 15%, and "Lots" 30%. The rest is charged at the day rate.
• Tariffs with more than one cheap period are worked out at the cheapest rate. This may slightly flatter tariffs whose cheapest window is short.
• Daily limits on cheap electricity, where a tariff has one, are applied. Anything over the limit is charged at the day rate.
• Car efficiency figures in our car list are typical real-world figures for mixed driving across the year, rounded. Winter efficiency is lower.
• Prices include VAT. We use the direct debit price. We don't include gas.

Smart-controlled tariffs

Some tariffs (for example Intelligent Octopus Go) let the supplier decide when your car charges. They only work with certain cars and chargers. If you tell us your setup is compatible, or you're not sure and your car or charger make is on the supplier's list, we count your car charging at the cheap rate. Otherwise we mark the tariff "Not suitable for your setup": we show it, priced as if you couldn't use the cheap rate for your car, but we don't rank it.

These tariffs sometimes give extra cheap slots during the day. We don't count those, so your real cost could be a little lower.

Comparing with the price cap

"Saving vs price cap" compares each tariff with Ofgem's price cap rates for your region this quarter, using exactly the same electricity use. The cap is what most people on a standard variable tariff pay. If the cap for the current quarter hasn't been added yet, we don't show this saving.

Where prices come from

• Octopus Energy: imported automatically every day from Octopus's public price data, for all 14 regions.
• Other suppliers: checked by hand against the supplier's own published prices.
• Price cap: entered by hand from Ofgem's published figures each quarter.
• Your region: found from your postcode using Octopus Energy's public region lookup. We don't store your postcode.

Every result shows when we last checked it. We hide any tariff not checked in the last 60 days. Because Octopus is updated automatically, its tariffs are more likely to be up to date than others. That is not a recommendation.

Public charging

For drivers who can't charge at home, we estimate a month of public charging:

Electricity per month (kWh) = miles per week × 52 ÷ 12 ÷ miles per kWh ÷ charging efficiency
Charging efficiency          = 90% on rapid and ultra-rapid, 85% on slow and fast
Pay as you go                = kWh × price (peak or off-peak, by your answer) + connection fees
Charges per month            = kWh ÷ 30 (rapid, ultra-rapid) or ÷ 15 (slow, fast)
Subscription                 = monthly fee + kWh × member price + connection fees
Pays for itself above        = fee ÷ (pay-as-you-go price − member price), shown in miles

• Charger speeds: slow is under 8 kW, fast 8–49 kW, rapid 50–149 kW, ultra-rapid 150 kW and above.
• Prices vary by site. Where we read a network's open data, we show the typical (middle) price across the sites we read, with the cheapest and dearest, and how many sites we counted. For very large networks we read a sample of sites each day.
• VAT: open data gives prices before VAT, so we add VAT (20% unless the data says otherwise).
• Membership and subscription prices are rarely in open data, so we check them by hand on the network's website.
• Overstay, idle and per-minute fees are shown as a warning but not added to the cost.
• Price changes are recorded each time a price we hold changes, so each network page shows a history. Fixes to our own mistakes are marked as corrections.
• Safety checks: if an imported price is below 10p or above £1.50 per kWh, or changes by more than 30% in a day, we hold it back for a person to check.
• Networks and prices not checked in the last 60 days are hidden.

Some networks publish open data under the Public Charge Point Regulations 2023, and we read it automatically. We credit them on their network page. See public charging prices.

Home vs public and the price index

• Home overnight rate: in each region, the cheapest overnight rate among EV tariffs checked in the last 60 days; we show the middle value (median) across regions.
• Public rates: each network's cheapest pay-as-you-go price at that speed, checked in the last 60 days; we show the median across networks.
• Monthly costs count car charging only (the home standing charge is paid either way) and allow for energy lost while charging: 10% at home and on rapid chargers, 15% on slower public chargers.
• Every figure says how many regions or networks it's based on. If there aren't any, we say "not enough data" instead of guessing.
• The price index takes these figures on the 1st of each month, at 3.5 miles per kWh, and never changes past months.

Price alerts

If you set up a price alert, we re-run your comparison each day after prices update. We only email you when a tariff checked in the last 30 days would cost at least £50 a year less than your best result when you signed up (or than the last tariff we told you about), and never more than once a month.

What we don't do

• We don't cover every tariff or every supplier. We are not "whole of market".
• We are not accredited by Ofgem.
• We don't take commission. Supplier links are plain links.
• We don't give financial advice. Check final prices and terms with the supplier before switching.

Questions

Spotted a mistake? Tell us.