Half-hourly electricity prices explained
On a half-hourly tariff, the day is split into half-hour periods and each one has its own price. Your smart meter records how much electricity you use in each period, and your bill adds up the cost of every half hour.
48 prices a day
A normal day has 48 half-hour periods, starting at midnight, 00:30, 01:00 and so on. The day the clocks go forward has 46, and the day they go back has 50. Each price is a unit rate in pence per kilowatt-hour (p/kWh). One kilowatt-hour is the energy a 1 kW appliance uses in one hour.
How your bill is worked out
For each half hour, the cost is the electricity you used in that half hour times that half hour’s rate. Then a daily standing charge is added.
An illustrative example (made-up prices, not today’s rates): charging an electric car on a 7 kW home charger for two hours uses about 14 kWh. Across four half hours at an average of 10p/kWh, that costs about £1.40. The same charge across four half hours averaging 30p/kWh costs about £4.20. The energy is the same; only the timing changed.
Reading a day of rates
- Look at the average over the whole time you need, not just the single cheapest half hour. A two-hour job spans four half hours.
- Only rates that have been published are certain. The next day’s rates usually appear once a day, in the afternoon; anything further ahead is a forecast.
- Prices differ by region. Great Britain has 14 electricity regions, and dynamic tariffs usually set a separate rate for each, partly because network costs differ.
- Check whether the rates you are reading include VAT, so you compare like with like.
Half-hourly readings and your data
Half-hourly prices only work if your supplier collects half-hourly readings from your smart meter, which you agree to when you join a tariff like this. The readings show when you use electricity, so read your supplier’s privacy information to see how they are used.
New to dynamic tariffs? Start with what an Agile-style tariff is, then see how to use cheap slots.
Plan with the day’s rates on your iPhone
Octomiser shows the current half-hourly rate and the rates still to come, finds the cheapest window for the time you need and keeps live rates in Home and Lock Screen widgets. Today it works with Octopus Energy accounts in the UK, including the Agile tariff.
Download on the App Store