How to calculate the cost of electricity in your home

The northern hemisphere is heading into winter. Stating the obvious here, but with the temperatures and levels of daylight going down, the electricity bills like to go up. As a customer, can you calculate how much you will end up spending?

I am a creature of warmth and good lighting. Nothing thrills me less than cold, dark spaces. Therefore, my bills can skyrocket during the cold season. However, knowing how electricity billing actually works allows me to:

  • Predict the costs increase fairly accurately
  • Make adjustments to avoid overspending beyond acceptable level

My household consists of myself, one adult male (aka the handsome boyfriend) and two cats (they’re adorable, go see their Instagram). We have LED lighting in the kitchen and on my nightstand, energy saving light bulbs in all other rooms (7 additional bulbs in total across the flat). The constantly-running items include the power connection to the combi boiler, a CatMate water fountain, a fridge, broadband router, a TV and a decoder box (mainly on standby) and power to the oven clock and one laptop with a poor battery. Items used multiple times per day include a kettle and a microwave. Items used 3-4 times per week include the vacuum (we use cordless Dyson V6 Absolute which runs for 20 minutes and charges to full in 3h 30m, don’t buy it), a dishwasher, washing machine and various electronics needing charging. Items used once per week or less include charge for electric toothbrushes (we use Sonicare DiamondClean which last up to 3 weeks on one 24h charge, we have two of these and they’re great but prone to breakdowns), Philips Lumea which needs charging every month or so, a hairdryer and a curling wand. Why am I telling you all this? Because I know what needs feeding in my house and you should know as much for your own house.

Every single item listed here consumes a specific amount of wattage it will consume when connected to electricity and in use. The amount of watt required to power the item is usually listed on the box. As example, the wattage of my kettle is 3000.

The costs of energy are charged in units called kilowatt hour (kWh) but are not actually related to the number of kilowatts you are using per hour. 1 kWh equates to 1000-watt appliance running for one hour. My kettle, needing 3000 watts to run would rack up 1 kWh in just 20 minutes of constant operation. If it run for one hour constantly, it would equate to 3 kWh. I am a tea drinker and use it for about 20 minutes per day.

Most electricity bills are made out of two things:

  • A standing charge which covers the cost of supply being available for your property
  • Cost calculated on the basis of the number of Kilowatt Hours (kWh) your household has consumed in any given billing period

My electricity tariff currently costs £0.03523 per kWh on top of a daily £0.32p standing charge. This means that it costs me £0.35523 per day to use the kettle. Doesn’t seem much, but that’s £10.66 per month.

And what about the cost of lighting? Let’s say I am a boring little darling and I spend my evenings sitting in the living room where we have two lightbulbs in use. One for the ceiling lamp (15W spiral energy-efficient bulb) and one for the floor lamp (42W halogen bulb). Let’s say that the ceiling lamp runs from the moment I land on the sofa at 8pm and stays on until 11pm. The floor lamp will come on when I wish to read, let’s say for one hour during that evening. In the scale of one month, my cost calculation would look like this:

(3 hours*15W + 1 hour*44W) * 30 days = 2670W.

That’s 2.67 kWh or £0.96, which is not a lot of money. But if I were to run an electric heater for 3 hours per day which is 2000W, the cost would equate to 180 kWh per month or £6.34, not including the standing charge. If you have a heater like this running in every room for few hours per day…costs stack up from small sums to big sums fast.

I hope the examples above help to explain how electricity costs work. Here is a handy little electricity cost calculator in excel.

And before you finish reading this post, there is one more recommendation I have for you – shop for energy prices and do not be afraid to change your energy supplier for a better deal. In the UK utility companies have been raising prices like there is no tomorrow, so if your energy costs seem too expensive, keep looking until you find a cheaper deal.

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