Electricity cost calculator (UK): estimate your kWh costs

Work out what an appliance costs to run, estimate your daily and monthly electricity bill, and see how unit rates, standing charges and your meter type affect the total.

  • Use simple inputs: watts (or kW), hours used, and your electricity unit rate (p/kWh)
  • Includes UK bill basics: standing charge, day/night rates, and smart meter readings
  • Compare tariffs with whole-of-market quotes (no obligation)
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Estimates only. Your actual costs depend on your tariff, meter type, usage patterns, and region. Always check your latest bill or supplier account for your current rates.

Fast answer: Electricity cost calculator

An electricity cost calculator estimates what you’ll pay by multiplying your usage in kWh by your unit rate (p/kWh), then adding any standing charge. The key number is: cost per day = (kWh used × unit rate) + standing charge. Use your bill for accurate rates, especially for Economy 7 and smart tariffs.

Quick formula

Watts → kW: W ÷ 1000. kWh: kW × hours. Cost: kWh × p/kWh.

What most people miss

Standing charges, day/night split (Economy 7), and that “kWh” is energy used, not the appliance’s wattage.

Best next step

If your estimated monthly cost looks high, compare tariffs and payment methods—prices can vary by region and meter type.

Tip: To calculate a whole bill, you’ll need your unit rate(s) and standing charge. These are on your electricity bill or online account. If you’re on a smart time-of-use tariff, rates can change by time and day.

Calculate your electricity costs (and get quotes)

Use the steps below to estimate appliance costs and your total electricity spend. If you want, you can also request a whole-of-market comparison quote—useful if your unit rate or standing charge is higher than you expected.

Step-by-step (appliance running cost)

  1. Find the power in watts (W) on the label or manual (e.g., 2,000W heater).
  2. Convert to kW: watts ÷ 1000 (2,000W = 2kW).
  3. Multiply by hours used to get kWh (2kW × 3 hours = 6kWh).
  4. Multiply by your unit rate (6kWh × 24p = £1.44). Add standing charge only when estimating a full day/month bill.
Economy 7 / dual-rate meters: split your usage between day and night rates. Storage heaters, immersion heaters and EV charging often drive the night share.

Two realistic UK scenarios (with numbers)

Scenario 1: Standard single-rate tariff

Assumptions (example only): unit rate 24p/kWh, standing charge 60p/day, household uses 10kWh/day.

Daily usage cost
10kWh × 24p = £2.40
Daily total incl. standing charge
£2.40 + £0.60 = £3.00/day
Estimated monthly total (30 days)
£3.00 × 30 = £90/month

If your actual unit rate is higher, the bill rises quickly: each extra 1p/kWh adds ~10p/day at 10kWh/day.

Scenario 2: Economy 7 (day + night rates)

Assumptions (example only): day rate 28p/kWh, night rate 14p/kWh, standing charge 60p/day, total use 12kWh/day with 40% at night.

Night usage (40% of 12kWh)
4.8kWh × 14p = £0.67
Day usage (60% of 12kWh)
7.2kWh × 28p = £2.02
Daily total incl. standing charge
£0.67 + £2.02 + £0.60 = £3.29/day (≈ £99/month)

Economy 7 tends to suit homes that can shift a meaningful share to the night rate (e.g., storage heating, EV charging). If most use is daytime, it may cost more.

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How to compare correctly
Privacy: We use your details to provide quotes and support your request. Rates and availability vary by region, supplier and meter type.

Comparing electricity prices: what to look at (UK)

A unit rate that looks cheap can be offset by a higher standing charge (and vice versa). If you’re comparing tariffs, check the full picture and make sure you’re comparing like-for-like for your meter type.

What changes your cost Why it matters What to check on your bill/quote
Unit rate (p/kWh) Main driver of cost for most households. Is it single-rate, day/night, or time-of-use?
Standing charge (p/day) You pay this even if you use little or no electricity. Compare daily charge and how it affects low usage homes.
Meter type Economy 7 and smart tariffs price electricity differently. Single rate vs dual rate; any special conditions for smart tariffs.
Payment method Direct Debit, prepay and cash/cheque can price differently. Is the quote for your actual payment type?
Region (network area) Standing charges and unit rates can vary across Great Britain. Postcode-based rates; don’t compare headlines from other areas.
Exit fees / contract terms May affect whether switching now is worthwhile. Any early exit charges, fixed end date, and price guarantees.

Decision checklist: who this calculator suits

  • Homeowners and tenants who want a quick appliance running-cost estimate
  • Households comparing single-rate tariffs using bill rates (p/kWh + p/day)
  • Economy 7 users who know (or can estimate) their day/night split

When a calculator is less reliable

  • Smart time-of-use tariffs where the unit rate changes by time/day
  • Homes with solar/export, batteries, or complex heating controls
  • If your “watts” figure is a maximum but the device cycles on/off (e.g., fridges)
Practical tip: If you’re unsure about your unit rate, use the electricity section of your latest bill. You may see “unit rate”, “standing charge” and (for Economy 7) separate “day” and “night” lines.

Common pitfalls, exclusions and cost gotchas

Electricity pricing in Great Britain is usually straightforward, but a few details can skew estimates. Use the cards below to sanity-check your numbers before making decisions.

Standing charge isn’t optional

If you only calculate kWh × unit rate, you’ll understate your bill—especially for low-usage homes, second homes, or vacant periods.

Watts are often “max”, not “typical”

Kettles, ovens and heaters can run near max power. Fridges, freezers and boilers cycle, so real kWh is usually lower than max watts × hours.

Economy 7 hours vary by region

Night-rate times can differ by meter and area. Don’t assume the same hours as a neighbour—confirm with your bill, supplier, or meter settings.

Price cap isn’t a “cap on your bill”

Ofgem’s price cap limits unit rates and standing charges for typical tariffs, not the total you pay. Higher usage still means a higher bill.

VAT and discounts

Domestic energy is typically charged with VAT. Some tariffs include discounts or bundle conditions—always check the quote’s assumptions.

Prepayment meter differences

Prepay tariffs can have different pricing. If you’ve recently changed meter/payment type, your old bill rates may no longer apply.

Important: This guide is for home energy only. Business electricity contracts, half-hourly settlement and commercial tariffs need a different approach.

FAQs

How do I calculate electricity cost per kWh in the UK?

Check your bill for the electricity unit rate in pence per kWh (p/kWh). Your energy cost is kWh used × unit rate. To estimate a whole-day bill, add your standing charge (p/day). Economy 7 has separate day and night unit rates.

How much does a 2,000W heater cost to run for 3 hours?

A 2,000W heater is 2kW. Over 3 hours it uses 6kWh (2 × 3). Multiply by your unit rate. For example, at 24p/kWh it costs £1.44 (6 × £0.24). This is the usage cost and doesn’t include your standing charge.

What’s the difference between kW and kWh?

kW is power (how fast electricity is used). kWh is energy (how much electricity is used over time). If a 1kW appliance runs for 2 hours, it uses 2kWh. Your electricity unit rate is charged per kWh.

Do I need to include the standing charge in my calculation?

Yes if you’re estimating your total bill. The standing charge is a daily amount you pay regardless of usage, so it can be a big part of costs for low-usage households. If you’re only estimating an appliance’s running cost for a few hours, you typically use just kWh × unit rate.

Are electricity rates the same across the UK?

No. Electricity unit rates and standing charges can vary by region (network area), payment method (Direct Debit vs prepay), and meter type (single rate vs Economy 7). That’s why using your own bill rates (or postcode-based quotes) gives a more accurate estimate.

Does the Ofgem price cap mean my bill can’t go above a certain amount?

No. The Ofgem price cap limits the maximum unit rate and standing charge for typical capped tariffs, not the total you pay. Your bill still depends on how many kWh you use. For the latest explanation, see Ofgem’s guidance on the price cap.

Can I use this calculator if I have a smart meter?

Yes. If you’re on a standard single-rate smart tariff, use your normal unit rate and standing charge. If you’re on a time-of-use tariff (rates change by time and day), a simple calculator becomes less precise—use your supplier’s usage data by time band for better results.

Will switching electricity supplier change my meter or disrupt my supply?

In most home switches, your electricity supply stays on and you usually keep the same meter. You’ll typically provide meter readings (or smart readings are used) around the switch date. Always check the new tariff’s terms, including any exit fees or meter requirements.

Need your rates? Your unit rate(s) and standing charge are shown on your electricity bill, and often in your online account/app. If you can’t find them, Citizens Advice explains where to look on a bill.

How we assess this (methodology) + editorial trust

Editorial details

Written by
EnergyPlus Editorial Team
Reviewed by
Energy Specialist
Last updated
July 2026

Assumptions we use in the examples

  • Appliance energy use is estimated from rated watts and time used (real usage can be lower/higher depending on cycling, thermostat control, and user behaviour).
  • Tariff estimates use a simple bill model: (kWh × unit rate) + standing charge.
  • Economy 7 estimates assume you can reasonably estimate your day/night split (e.g., 40% night). Your real split may differ.
  • All figures are illustrative and not a guarantee of your bill or savings.
Limitations: If you’re on a smart time-of-use tariff, your unit rate can change by half-hour or by set time bands. For those tariffs, the most accurate method is to use your supplier’s consumption breakdown by time band and apply the matching rates.

Sources (UK)

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Updated on 2 Jul 2026