EV charging cost calculator for flats and apartments

A flat resident may pay a tariff set through a landlord, managing agent, freeholder, parking operator, or building-selected charge point provider. That tariff can differ from domestic electricity price and from public price shown for same network brand. Start with price notice, app screen, resident agreement, or provider statement for your exact charger.

Record building, charger identifier, payment route, tariff date and displayed units. Keep separate evidence when one notice says 49p/kWh but another adds platform, occupancy, parking, or session charges. ChargeWindow calculates values you enter; it does not fetch live prices or decide which contract term controls billing.

Energy price is only one input. Copy every charge that could reach the bill for the session you are modelling. Keep units and trigger wording intact so a per-minute amount cannot be mistaken for a fixed charge.

First convert the energy rate into pounds and multiply by energy delivered. Add each fixed charge once. For a time charge, calculate only the minutes or hours that meet the provider trigger. For an idle charge, subtract any stated grace period before applying the rate, then apply a stated cap if the tariff contains one.

Keep intermediate amounts visible. A single total without its components is hard to check against a receipt and makes it easy to apply the wrong clock.

Assume a resident adds 28 kWh at £0.49/kWh. The tariff also applies a £1 session fee, 2p per connected minute for a three-hour stay, and 10p per idle minute after a ten-minute grace period. The car remains connected for thirty minutes after charging ends, so twenty idle minutes are billable.

Session total is £20.32. Dividing by 28 kWh gives 72.6p/kWh effective—23.6p/kWh above headline energy rate. At vehicle consumption of 28 kWh per 100 miles, same session costs £20.32 per 100 miles.

This is an illustration, not a current provider price. Replace every value with tariff evidence for your charger and test the time triggers before relying on the result.

Connected, charging, parking, and idle time are different measurements. A charge can start when you plug in, when energy begins, when charging reaches a target, when charging stops, or after a grace period. It may stop when the app session ends, when the cable is removed, or when the vehicle leaves the bay. Provider wording controls the calculation.

If the tariff gives a rate but no trigger, grace period, stop condition, or cap, mark that amount unresolved. Ask the provider or building manager for complete wording. A confident-looking estimate built from an assumed trigger is less useful than an honest incomplete one.

UK Public Charge Point Regulations guidance says public charge point operators must clearly display the maximum charging-session price in p/kWh and include fixed charging fees such as connection or transaction fees in that displayed maximum. Separate parking fees and overstay charges are treated differently in the guidance.

A resident-only charger behind a tenancy, lease, parking, or building access arrangement may not be a public charge point. Do not assume public-point requirements settle a restricted building tariff. Use them to understand pricing concepts, then check your resident contract, charger terms, and provider explanation for the route that applies.

Keep tariff evidence and calculation beside final receipt. Match delivered kWh, billed minutes, grace period, fixed charges and parking line by line. A difference may come from rounded billing units, changed price, different clock trigger, or fee omitted from notice you used.

Do not force receipt to fit estimate. Mark unexplained line, keep screenshot or statement, and ask provider or building manager which tariff version and event timestamps produced charge.

Run the same tariff against a routine charge, a small top-up, and a longer stay. Fixed fees usually weigh more heavily on small sessions. Connected-time and idle fees can dominate when the vehicle remains plugged in after energy delivery slows or stops. Keep energy, stay length, idle exposure, and payment route constant when comparing two tariffs.

ChargeWindow’s £29 calculator returns session total, effective £/kWh, and cost per 100 miles from manual tariff inputs. It stores one tariff locally in browser and creates local calculation receipt. It does not promise savings, interpret contracts, or replace current provider price shown before charging.