How these numbers are worked out

Every figure on this site is labelled with where it came from. Nothing is modelled from a guessed efficiency unless it says so.

Three labels, used consistently

The mistake almost every charging calculator makes

The obvious way to work out charging time is to divide battery capacity by charger power. For a BYD Atto 3 on an 11 kW supply that gives 60.48 ÷ 11 = 5 h 30 min.

BYD's own figure is 6 h 30 min. The difference is not rounding. Over that time the meter records about 18% more energy than the pack is rated to hold. Part of that is electricity lost as heat in the onboard charger, in the battery management system and in thermal conditioning; part may be the gap between rated and usable capacity, which BYD does not state. The split is unknown, and this site does not guess it. Either way, a calculator that divides capacity by power will tell you the car charges faster and costs less than it does.

What this site does instead

Rather than assume an efficiency figure, the calculation starts from the manufacturer's published charge time and works backwards to the energy that must have passed through the meter:

BYD's wording for the 6 h 30 min figure is Overnight charging from an almost empty battery to full range can be completed in just 6.5 hours. "Almost empty" is not a stated percentage, and the figure is quoted here as BYD states it.

There is no published 7 kW figure for this car, which is awkward, because 7 kW is what most single-phase British homes deliver. Rather than invent one, this site scales from the 11 kW figure and labels the result estimated. Charge times near 8 h 38 min circulate widely for this car; that is 60.48 divided by 7, and it implies the car draws less energy from the wall than the battery holds, which cannot happen.

This matters more than it looks. BYD publishes 60.48 kWh as the battery capacity but does not say whether that is the gross pack or the usable portion. The owner's manual lists the pack at 150 Ah, and 60.48 divided by 150 is 403.2 V, a plausible nominal pack voltage that BYD itself does not publish: the capacity figure reads as amp-hours times nominal volts, a nameplate number rather than a measurement of energy recovered. Deriving wall energy from charge times sidesteps the question entirely. Both the unknown usable capacity and the unknown charging efficiency are absorbed into one number that comes straight from the manufacturer, and the site never has to claim a usable capacity it cannot verify.

Vehicle limit, charger limit, supply limit

Three separate ceilings decide how fast a car actually charges, and the lowest one wins:

• What the car's onboard charger accepts — 11 kW for the Comfort and Design trims of this model
• What the wallbox or charge point is rated at
• What the building's electrical supply can deliver

Quoting the first as if it were the answer is how specification sheets mislead people. The BYD Atto 3 accepts 11 kW, but that needs a three-phase supply, and most homes in the United Kingdom are single-phase. On a normal domestic supply the car charges at up to 7 kW, and the site defaults to that.

Peak power is not average power

BYD's rapid charging claim for this car is 30–80% in 29 minutes verified, measured on a 150 kW charger. That 150 kW belongs to the charge point, not to the car. The car's own peak is 88 kW verified, which BYD UK publishes on its Atto 3 page. Quoting a charge point's rating as if it were the car's is a common way specification tables overstate performance.

Across that interval the average works out at roughly 63 kW estimated: it assumes half the rated capacity moves between 30% and 80%, and rated capacity is not usable capacity. It sits below the 88 kW peak, as an average should: a peak is held briefly, not across the whole interval, so the two figures are consistent.

Note also where BYD starts the clock. This interval runs from 30%. Set against a claim quoted from 10% to 80%, it leaves out the first 20 points of charge, which are the fastest part of the curve, so a 30% start skips the easiest work. The figure is only comparable with a rival's if that rival measured the same window; check the window before reading across a table.

Only the published interval is presented as fact. Any other range is scaled from it and labelled estimated, because publishing a full charge curve the manufacturer never released would be inventing data.

Time-of-use tariffs are modelled minute by minute

An off-peak tariff only applies during its window. Intelligent Octopus Go runs from 23:30 to 05:30, which is 6 hours, and at 7 kW that window can deliver about 42 kWh. A full charge at 7 kW needs around 71.4 kWh estimated, scaled from the 11 kW time, so it does not fit.

The calculator simulates the session at one-minute resolution, bills each minute at whichever rate applies, and shows the overflow separately. Treating the whole session as off-peak understates a 10–80% charge by about 27%.

• BYD Atto 3 charging cost in the United Kingdom

Prices are dated, not averaged

Domestic prices use the Ofgem price cap in force on the date the page was built, currently £0.2632/kWh from 2026-10-01. Every published cap period is stored, so the site changes over automatically when a new one takes effect.

One caveat on comparing cap periods: VAT on domestic electricity in Great Britain drops from 5% to zero on 2026-10-01, until 2027-03-31. Caps quoted either side of that date are not directly comparable, and a rise that looks small on the headline rate is larger underneath it.

Public charging prices are attributed to a named operator and never presented as national averages, because they are not. Rates vary by operator, by site and in some cases by local authority.

The standing charge is excluded from charging costs. You pay it whether or not you plug in, so it is not part of the cost of a charge. It belongs in an annual running-cost model, where it will appear when that tool is published.

What is measured, and what is not

The specifications and prices above come from manufacturers and regulators. Separately, this site logs real data from one BYD Atto 3: every charging session, sampled journeys and a monthly snapshot of the odometer and lifetime consumption. A battery capacity check every two months is part of the protocol; none has been logged yet, and the first will appear on the owner-data page with its date. That logged data is presented as its own thing and never blended into manufacturer figures without saying so.

Corrections

If a figure here is wrong, it should be fixed rather than defended. Errors are corrected in place and the change is noted at the foot of the affected page. Get in touch if you find one.

Corrected 2026-09-06. This page previously gave 9 h 42 min as BYD's official 7 kW charge time for the BYD Atto 3. That figure could not be traced to BYD in the UK launch specification, the owner's manual or the sales brochure, and has been removed; the worked example now uses the 11 kW time, which BYD does publish.

Corrected 2026-09-06. The rapid charging section previously described 150 kW as the car's peak acceptance. It is the rating of the charge point BYD used, and has been corrected.

Corrected 2026-09-12. This page previously said BYD does not publish what the BYD Atto 3 accepts at peak DC power. BYD UK's Atto 3 page states "a charging capacity of DC 88kW", and that figure is now shown as verified with that source. It had earlier been removed from this site because no manufacturer document could be traced for it at the time.

Corrected 2026-10-01. Five things on this page overstated what is known. It said that around 18% of what the meter records never reaches the battery; 18% is how much more the meter records than the pack is rated to hold, and how much of that is loss rather than unusable capacity is not published, so the sentence now says so. It called 403.2 V the nominal pack voltage; BYD publishes no pack voltage, and the figure is now presented as implied by the published kWh and Ah. It said the same car sold in other markets quotes a comparable rapid-charging time against a much lower charge point rating; no BYD document publishes such a time, and the car sold elsewhere carries a different DC module, so the sentence has been removed. And the 63 kW average was shown without the estimated badge it carries on the other pages. It also described a battery capacity check as something already logged; none had been. The same day, the passage on charging windows stopped saying that most manufacturers quote from 10% and that almost none measure from 30%: neither claim had been sourced. It now says only that two intervals compare when they cover the same window. The first correction above was dated 2026-09-02 until today; that was the day this page went live still carrying the figure that correction describes, and the fix was made on 2026-09-06, so the note now carries that date. The tariff section also set the cheap window against the energy derived from the 11 kW time; it now uses the 7 kW figure, which is scaled and labelled estimated like everywhere else.