Home▸Energy & Thermodynamics▸Electricity Bill Calculator — Standard vs Off-Peak Tariff

🔋 Electricity Bill Calculator — Standard vs Off-Peak Tariff

Model a UK household electricity bill: standing charge plus unit rate, then compare it against an Economy-7-style off-peak tariff that shifts usage to a cheaper night rate.

Energy & Thermodynamics3DEasy60 FPS

The Model

Annual bill = standing charge × 365 days + daily kWh × 365 × unit rate. The standing charge is fixed regardless of consumption — it funds network maintenance and metering — while the unit-rate cost scales linearly with how much electricity you actually use, which is normally the larger share of the bill for an average household.

Economy 7 & Off-Peak Tariffs

An off-peak (Economy 7-style) tariff charges a cheaper rate during a set night window, usually seven off-peak hours. This simulation lets you set what fraction of your daily usage happens at night and shift that portion to the off-peak rate, while the rest stays on the standard day rate — mirroring how a real dual-rate meter splits your consumption.

When Switching Pays Off

Off-peak plans only save money once enough usage moves to the cheap window: if the night-usage fraction is small, or the day rate and night rate are close together, the standing charge (unchanged either way) dominates and there is little or no saving. Shifting laundry, dishwashing, EV charging or storage heating to the night window is what makes an Economy 7-style tariff pay off in practice.

About this simulation

This simulation models a typical UK domestic electricity bill: a fixed standing charge that applies every single day plus a unit rate charged per kilowatt-hour consumed. It then re-runs the same annual usage under an Economy-7-style off-peak tariff, where a chosen fraction of daily usage is shifted onto a cheaper night rate, so you can see exactly how much a dual-rate meter would save — or cost — a given household.

🔬 What it shows

Two stacked bars: the standard tariff on the left and the off-peak plan on the right, each split into a grey standing-charge segment and a coloured usage-cost segment. A pulsing marker sits on top of whichever bar currently comes out cheaper, so the winner is always obvious at a glance.

🎮 How to use

Set your daily usage in kWh, the standard unit rate and the daily standing charge to match a real bill, then drag the night-usage fraction and off-peak night rate to see how much of a saving an Economy-7-style dual-rate meter would actually deliver for that usage pattern.

💡 Did you know?

The standing charge is identical on both bars in this model — it doesn't change if you switch tariffs — so every pound of saving here comes purely from moving usage into the cheaper night window. If your night-usage fraction is low, an off-peak tariff can easily end up costing more, not less.

Frequently asked questions

How is the annual electricity bill calculated here?

Annual bill = standing charge (pence per day) × 365, plus daily kWh usage × 365 days × unit rate (pence per kWh), converted to pounds. This mirrors how UK suppliers itemise a bill: a fixed daily charge for being connected to the network, plus a variable charge for the energy actually consumed.

What is an Economy 7 / off-peak tariff?

It's a dual-rate tariff that charges a cheaper unit rate during a set off-peak window, typically about seven hours overnight, and a standard (often slightly higher) rate during the day. It rewards households that can shift usage — such as storage heating, EV charging, or running appliances overnight — into that cheap window.

Why might switching to an off-peak plan cost more, not less?

If only a small fraction of your usage happens at night, most of your consumption still falls on the daytime rate, and any premium built into that daytime rate isn't offset by the small amount of cheap night usage. The off-peak plan only pays off once a meaningful share of consumption is genuinely shifted into the off-peak window.

Why does the standing charge take up so much of a small bill?

The standing charge is fixed at roughly 30-70 pence a day regardless of usage, so for a household with low consumption it can represent a large share of the total bill. As usage rises, the standing charge stays constant in pounds but shrinks as a percentage of the total, because the usage cost grows in proportion to consumption.

Does this model include VAT or government levies?

No — this is a simplified illustrative model of the two core components (standing charge and unit rate) that make up the bulk of a domestic bill. Real bills also include VAT (charged at a reduced 5% rate on domestic energy in the UK) and various levies, which this simulation does not itemise separately.

⚙ Under the hood

Model a UK household electricity bill: standing charge plus unit rate, then compare it against an Economy-7-style off-peak tariff that shifts usage to a cheaper night rate.

Three.jselectricity billUK energyEconomy 7tariff comparison

3D · Three.js / WebGL renderer · 60 FPS target · runs fully client-side, no install