Electricity Cost Calculator

How to Find Wattage?

Check the label on the back or base of the appliance — wattage is usually printed there or in the manual. If listed in kilowatts (kW), multiply by 1000 for watts. A kettle is 2,000–3,000W. A fridge is 150–400W running average. An EV charger (7kW wallbox) is 7,000W.

What should I know about UK Tariff Rates?

The Ofgem price cap sets the unit rate each quarter. As of early 2025 the UK unit rate is around 24–28p/kWh. Check your energy bill's 'unit rate' line for your exact figure. Some tariffs have different day/night rates.

What's the key thing to understand about Biggest Energy Users at Home?

Electric shower (9,500W), electric hob (2,000W per ring), tumble dryer (2,500W), dishwasher (1,200W per cycle), EV charger (7,000W). These items dominate most household energy bills — understanding their real cost helps prioritise savings.

What should I know about Energy Efficiency Priorities?

Home energy improvements should be prioritised by payback period. Quickest payback: draught proofing (£50-200 cost, saves £60-100/year — under 2 years). Loft insulation (£300-500 DIY, saves £150-200/year — 2-3 years). Switching to LED lighting (under £100, saves £40-60/year — under 2 years). Longer payback: cavity wall insulation (3-5 years). New efficient boiler (5-10 years). Solar panels (7-15 years). Heat pump (10-25 years at current energy prices). For homes eligible for ECO4 funding, the payback period on insulation measures can be reduced to near-zero, since the scheme covers some or all of the installation cost for qualifying low-income and vulnerable households — check eligibility on GOV.UK before paying for insulation work out of pocket.

What should I know about Standing Charges on Your Bill?

This calculator estimates the running cost of a single appliance based on its wattage, hours of use, and your unit rate — but your actual electricity bill also includes a daily standing charge, a fixed amount charged regardless of how much electricity you use, which covers the fixed costs of maintaining your grid connection. This means the cost-per-hour and cost-per-day figures here represent only the variable usage cost of the specific appliance you're checking, not your whole household bill. To estimate a full day's total electricity cost you'd need to add up the running cost of every appliance used that day, plus the standing charge on top. This calculator is most useful for comparing appliances against each other — for example, whether it's cheaper to run a tumble dryer or an electric heater for the same task — or for spotting which devices are quietly costing the most over a year, rather than for predicting your total bill directly from a single appliance figure.

What do I need to know about Standby and Phantom Power Use?

Many household appliances continue to draw a small amount of electricity even when switched off at the device but still plugged in, often called standby or phantom power. Televisions, set-top boxes, games consoles, and phone chargers left plugged in can each draw anywhere from 1-15W continuously, 24 hours a day. Run a device at just 5W through this calculator for 24 hours a day and you'll see it still adds a noticeable amount to an annual bill — small figures that add up across a household with a dozen or more standby devices. Games consoles and set-top boxes left in standby with 'quick start' or always-connected features enabled can be surprisingly high, sometimes rivalling the consumption of a device actually in use. Using a smart plug or a switched extension lead to fully cut power to groups of devices overnight or when away from home eliminates this waste. Running your most power-hungry appliances through a smart plug also lets you verify real-world wattage, since nameplate ratings on appliances are often the maximum draw rather than typical day-to-day consumption.

How Do Time-of-Use Tariffs Change Electricity Costs?

Time-of-use tariffs charge different rates for electricity depending on when it's used, rather than a single flat rate throughout the day, and shifting usage into cheaper windows can produce meaningful savings for households able to be flexible about timing. Economy 7-style tariffs, historically paired with storage heaters, offer a cheaper overnight rate (often around 11pm-7am) in exchange for a higher daytime rate, which only benefits households able to genuinely shift significant usage — like charging an EV or running a washing machine — into that overnight window. Newer smart and EV-specific tariffs often extend this idea with more granular time bands, sometimes including very cheap off-peak rates for several hours and a higher peak rate during early evening hours (typically 4-7pm) when national electricity demand is highest. The savings potential depends heavily on how much of a household's usage can actually be shifted: a household that mostly uses electricity for lighting and evening cooking — fixed by necessity to peak hours — will see limited benefit from time-of-use pricing, while a household with an EV, battery storage, or appliances that can be timer-delayed (dishwashers, washing machines, tumble dryers) can shift a substantial share of consumption into the cheap window. Before switching, it's worth totalling how much usage genuinely falls in flexible categories, since a time-of-use tariff's higher peak rate can leave inflexible households worse off overall.

Worked Example: Running Cost of a 2kW Heater for 3 Hours a Day

A 2kW (2,000W) electric heater run for 3 hours a day uses: energy = power (kW) × time (hours) = 2 × 3 = 6 kWh per day. At an illustrative unit rate of 27p per kWh (UK rates vary by tariff and change periodically — always use your own tariff's current unit rate for an accurate figure), daily cost = 6 × £0.27 = £1.62. Over a 90-day winter heating season used daily, that's £1.62 × 90 = £145.80 — a useful figure for comparing against the cost of an alternative heating approach, or for deciding whether a second heater in a rarely-used room is worth the running cost versus simply heating that room from the central system occasionally instead.

How Do I Read My Electricity Meter to Check Actual Usage?

A digital/smart meter typically shows a running total in kWh directly on its display, sometimes toggling between several screens (total import, possibly day/night rates on a dual-rate meter, and sometimes an instantaneous power reading in kW). To check real usage over a period, note the reading at the start and end of that period and subtract: the difference is the kWh consumed. For an older analogue (dial or digital-odometer-style) meter, read the digits left to right in the same way, ignoring any red digits or decimal fraction digits unless billing explicitly includes them. Comparing a reading taken immediately before and after running one specific appliance (with everything else in the house switched off at the wall where practical) is a simple, free way to measure a real appliance's actual consumption rather than relying on its rated nameplate wattage, which is a maximum figure and often somewhat higher than typical real-world draw.

How Do Economy 7 and Other Time-of-Use Tariffs Change the Calculation?

Economy 7 and similar time-of-use tariffs charge a lower unit rate during a fixed off-peak window (commonly around 7 hours overnight, hence the name) and a higher rate the rest of the day, in exchange for a (often slightly higher) day rate compared with a flat single-rate tariff. This only saves money if a meaningful share of usage can genuinely be shifted into the cheap window — storage heaters, immersion heaters on a timer, and EV charging are the classic loads worth timing to off-peak hours, while general daytime appliance use (cooking, lighting, most appliances) generally can't be shifted and is charged at the (often higher) day rate. Before switching to a time-of-use tariff, it's worth estimating what fraction of total kWh usage could actually move to the off-peak window — if it's a small fraction, a time-of-use tariff can end up costing more overall despite the attractive-looking off-peak rate.