How this works
Electricity is billed by the kilowatt-hour (kWh) — one kilowatt of power consumed for one hour. The maths is therefore simply (power in kW) × (hours used) × (rate per kWh). The fiddly bit is the unit conversion, since appliance labels are mostly in watts (a 60 W bulb, a 1,500 W kettle) while your bill is in kWh: 1,000 watts = 1 kilowatt, so a 60 W bulb on for 10 hours uses 60 × 10 / 1,000 = 0.6 kWh.
The widget lets you toggle the input between W and kW so you can type either unit naturally, then runs the cost for the period you specify ("hours per day × days") and also extrapolates a per-day and per-year figure. The per-year number is the useful sanity check — a £20/year bulb is fine, a £200/year heater is something to think about.
Typical 2026 rates are pre-filled per currency: ~$0.17/kWh in the US, ~£0.27 in the UK, ~€0.32 across most of the EU, ~¥31 in Japan. These are rough national midpoints — actual rates vary by region, supplier, tariff (standard vs. variable vs. time-of-use), and the standing charge that hits you regardless of usage. The calculator doesn't model the standing charge — for monthly bill prediction add yours on top (typically £5 – 20 in the UK, around $10 in the US).
The formula
Power in kW; if you enter W the widget converts (W ÷ 1,000). Rate is the marginal price per kWh, not the average bill — find it on a recent statement labelled "kWh rate" or "unit rate". Excludes the standing charge / abonnement / Grundgebühr (a flat daily or monthly fee that applies regardless of usage). To get a full bill, calculate cost here and add the standing charge multiplied by the number of days.
Example calculation
- 60 W LED bulb, 8 hours/day, for 30 days, at $0.17/kWh.
- Energy/day = 0.06 kW × 8 h = 0.48 kWh → 14.4 kWh in 30 days.
- Cost = 14.4 × 0.17 = $2.45 over 30 days. Yearly ≈ $30 (175 kWh/yr).
Frequently asked questions
Where do I find my actual rate per kWh?
On any recent bill or statement. Look for "unit rate", "price per kWh", "kWh rate", "electricity charge", "variable charge" or "energy charge" — the supplier-specific naming varies but the units are kWh-based. In the UK, your tariff comparison rate (the headline number Ofgem requires) is usually on page 1. In Germany, look for „Arbeitspreis". In France, look for « prix du kWh » under the Heures pleines / creuses line. In Japan, look for 従量料金単価. Use the marginal rate (the price of the next kWh), not the total bill divided by usage — those two differ once standing charges and tiered tariffs are in play.
What about appliances that cycle on and off, like fridges?
Use the rated wattage from the label and reduce "hours per day" to the duty cycle. A fridge labelled 150 W might only draw power 30 % of the time (the compressor cycles), so it averages 45 W continuous — enter 150 W and 7.2 hours/day to approximate. Better, find the annual kWh figure on the energy label (EU energy label, US Energy Guide) and divide it back into a per-day figure if you want to feed it into this tool — that number already accounts for the duty cycle and a representative usage pattern.
Why is my actual bill higher than this calculator says?
Three usual reasons. (1) Standing charge: a flat daily or monthly fee (£0.30 – £0.60/day in the UK, around $0.30 – $0.50/day in the US, €0.10 – €0.40/day across the EU) that applies regardless of usage. Add this on top — it adds up to £100 – £200 a year for a UK household. (2) Tax / VAT: most countries add 5 – 25 % VAT or sales tax on top of the unit rate; the rate shown on your bill may or may not already include it (in the UK 5 % VAT is included, in much of the EU it's added at the end). (3) Tiered tariffs: some suppliers charge a higher rate above a monthly threshold (typical in California, Japan, Spain) — punch in the rate that matches your usage tier.