Smart Meter Peak vs Off-Peak Savings Calculator

Smart Tariff Guide

What should I know about Time-of-Use Tariffs in the UK?

Smart time-of-use tariffs charge different rates at different times of day, incentivising shifting demand away from peak periods. Popular options in 2024: Octopus Agile: half-hourly variable rates linked to wholesale prices. Very cheap or even negative overnight (October-March). Best for flexible users with smart appliances. Octopus Go: fixed cheap rate at night (typically 7p-9p/kWh midnight-5am or 11.30pm-5.30am) with a standard daytime rate. Excellent for EV owners. Economy 7: old overnight tariff structure predating smart meters, still available on many suppliers' books — 7 hours of cheap overnight electricity (roughly midnight-7am, timing varies by region) with a higher day rate for the rest. Less flexible than newer smart tariffs since the cheap window is fixed rather than tracking actual demand or wholesale prices, but still worthwhile for households with storage heaters or immersion heaters that can be timed to run overnight.

What You Can Shift to Off-Peak?

Easily shiftable loads: EV charging (timer on charge points — biggest opportunity). Dishwasher (set delay start). Washing machine (set delay start). Tumble dryer (set delay start). Battery storage (charge overnight, discharge in peak periods). Immersion heater (timer to heat water overnight). Less flexible: cooking (mostly peak time). Heating (thermostat can be scheduled but thermal comfort limits). Lighting (mostly evening peak). The biggest single opportunity for most households: EV charging.

What do I need to know about Smart Meters and Agile Tariffs?

Smart tariffs require a smart meter (SMETS2). Contact your supplier if you do not have one — installation is free and suppliers are required to offer them. Smart meter does NOT change your tariff automatically — you must switch to a smart tariff after installation. Octopus Agile rates: published 4-5pm daily for the following day. Cheapest periods typically 2am-6am (grid demand lowest) and during high renewable generation (windy days). Plunge pricing: during very high wind output, rates sometimes drop below zero, meaning Agile customers are effectively paid to use electricity during those windows — running a washing machine, dishwasher, or EV charge during a plunge-pricing period can turn an ordinary chore into a small credit on the bill. The Octopus app sends alerts when plunge pricing is forecast.

Is a Smart Tariff Right for You?

Smart tariffs are best for: EV owners (large overnight charging demand). Houses with battery storage. Households with smart appliances (connected washing machine, dishwasher). People who work from home and can be flexible about when to run appliances. Smart tariffs are less suitable for: households that cannot shift any load (elderly residents who need heating/hot water during the day, no EV). Those with prepayment meters (limited compatibility). The key question: how much of your electricity usage can realistically be shifted to off-peak hours. A household that can move EV charging, laundry, dishwashing, and battery charging overnight stands to save significantly; one that mostly uses electricity during the day for cooking and general appliances, with no flexible loads, will see little benefit and may be better off on a simple fixed-rate tariff.

What's the key thing to understand about How Time-of-Use Tariffs Work with Smart Meters?

A smart meter's ability to record detailed, time-stamped energy usage data (rather than just a single periodic total reading) is what makes time-of-use tariffs possible — these tariffs charge different prices for electricity depending on the time of day it's used, typically offering significantly cheaper rates during designated off-peak windows (often overnight) in exchange for standard or even premium rates during peak demand periods (commonly early evening, when overall grid demand is highest). These tariffs can deliver meaningful savings for households able to shift a reasonable proportion of their usage into the cheap off-peak window — charging an electric vehicle overnight, running a washing machine or dishwasher on a timer during off-peak hours, or heating a hot water cylinder overnight for use the following day are all common ways to take advantage of off-peak rates. For households without much flexibility to shift usage timing — for example, a household where most electricity use happens unavoidably during the evening peak, such as cooking dinner and running lights and appliances when everyone is home — a time-of-use tariff can sometimes work out more expensive than a flat-rate tariff, since the premium charged during peak hours may outweigh the saving achieved on the relatively modest amount of usage that can realistically be shifted to off-peak times. Checking actual usage patterns, ideally using smart meter data from a recent period, before switching to a time-of-use tariff gives a much more reliable indication of likely savings than simply assuming any time-of-use tariff will automatically be cheaper.

What should I know about Smart Meter Data Privacy and Accuracy?

Smart meters transmit detailed usage data back to energy suppliers automatically, which raises legitimate questions some households have about privacy, though this detailed data is also precisely what enables more accurate billing (eliminating estimated bills based on guesswork between manual readings) and the more sophisticated tariff options, like time-of-use pricing, that can benefit cost-conscious households willing to shift usage patterns. Energy suppliers and network operators are subject to data protection regulations governing how smart meter data can be used and shared, and in most markets, households retain some control over how frequently detailed data is shared (for example, choosing between daily, half-hourly, or even more granular data transmission) and can request their supplier not to share certain data for purposes beyond billing, such as marketing — checking a specific supplier's privacy policy and data sharing options is worthwhile for anyone with concerns about this aspect of smart metering. On accuracy, smart meters are generally considered more accurate than older mechanical meters, since they remove the risk of misread dials or estimated bills based on historical usage patterns that may no longer reflect actual current consumption, though like any electronic device, they can occasionally develop faults or connectivity issues that temporarily prevent automatic readings from being transmitted — in these cases, suppliers generally revert to estimated billing until the fault is resolved, similar to the situation with older meters, so it's still worth periodically checking that bills are matching actual smart meter readings rather than assuming automatic accuracy indefinitely.

Worked Example: Flat Rate vs a Time-of-Use Tariff

Take a household using 3,500 kWh of electricity a year. On a standard flat-rate tariff charged at a typical unit rate of around 25p/kWh, the annual electricity cost is roughly £875, ignoring the standing charge. Now suppose the same household shifts 30% of its usage — the washing machine, tumble dryer, dishwasher and EV or battery charging — into an off-peak window on a time-of-use tariff, where off-peak units cost around 8p/kWh but peak and standard units cost more, say 30p/kWh to fund the cheaper off-peak rate: Off-peak portion: 1,050 kWh x £0.08 = £84 Remaining portion: 2,450 kWh x £0.30 = £735 New total: £819 That is only a modest £56 saving (around 6%) for shifting a third of usage — which is realistic for a household that cannot move space heating or most daytime cooking. A household that can also run an EV overnight and a home battery that charges off-peak and discharges at peak might shift 55-60% of usage, which widens the saving considerably because more kWh sit in the cheap band and less in the (higher) peak band that subsidises it.

Typical Time-of-Use Rate Bands

Smart time-of-use tariffs structure the day into bands rather than charging one flat rate, and the exact boundaries vary by supplier and by tariff generation (a half-hourly dynamic tariff moves these bands slightly every day based on wholesale prices).

The size of the saving opportunity depends on how "peaky" a tariff is — the bigger the gap between the cheapest and most expensive band, the more a household with EV charging, a home battery or flexible appliance use stands to gain, but also the more it risks losing if it cannot avoid running big loads (an electric oven, an immersion heater, a tumble dryer) during the expensive peak window. This calculator's shiftable-usage input is the single biggest driver of the result, which is why it is worth being realistic rather than optimistic about what can genuinely be rescheduled.