Home battery savings calculator

How to read these numbers

A home battery does not make electricity. It moves it in time. It stores cheap or free energy and hands it back when power would otherwise be expensive. So the saving on the right is really a measure of two things: how big the gap is between your cheap and expensive electricity, and how much of the battery you can genuinely fill and empty every day. Everything else is detail.

Start with the annual saving range, not a single number. We show a range on purpose, because your saving swings with how you live. A household that is out all day and charges the battery overnight on a cheap tariff will land near the top of the range. A household on a single flat rate with no solar and low evening use will land near the bottom, and sometimes below it. The truthful answer is that a battery pays best for busy homes with high usage, solar, or a time-of-use tariff, and pays back slowly for small, low-use homes on flat rates.

Why solar and a smart tariff change everything

The two biggest levers on this page are the solar toggle and the tariff toggle. With solar, the battery stores your own free daytime generation and gives it back in the evening, so you buy far less from the grid and stop exporting your surplus for a few pence. That is why a solar and battery pairing usually pays back in six to twelve years. Without solar, the battery still earns its keep, but only through the tariff. On a plan like Octopus Go you can charge overnight at roughly 7p and avoid peak rates of 24p to 35p, a spread of 15p to 17p on every stored unit. Heavy cyclers on a cheap overnight rate can see payback closer to three to eight years, while a battery on a flat rate with no solar can take much longer and is often not worth it.

Payback is a range, not a promise

Payback is simply the fitted cost divided by the yearly saving, so a faster saving means a shorter payback. Treat the years shown as a bracket. Real payback shifts with electricity prices, which have been volatile, and with how disciplined you are about charging on the cheap window. Batteries also lose a little capacity over time, typically 1.5 to 3 percent a year, and good LFP batteries are warranted for around 6,000 to 10,000 cycles or ten to twelve years. A sensible battery should comfortably pay for itself well inside its warranted life, but if the payback the calculator shows is close to or beyond that life, the honest conclusion is that the numbers do not stack up for your home yet.

Size to your home, not to the biggest box

Notice that jumping to a bigger battery does not simply multiply the saving. A battery only saves money on the energy it cycles, so an oversized unit in a low-use home spends half its life empty and the extra capacity never pays. As a rough guide, homes using under about 2,800 kWh a year suit a 5 kWh battery, most family homes at 3,000 to 4,500 kWh a year land on 10 kWh, and 13.5 kWh makes sense only for high usage, an EV, a heat pump, or when you want proper backup during a power cut. If the calculator caps your saving, that is the tool telling you the battery is larger than your bill can support.

A few honest caveats

There is 0 percent VAT on home battery storage in the UK until 31 March 2027, including standalone retrofits, which is already baked into the fitted costs above. Export rates and tariff availability move around, so check current terms rather than assuming last year's numbers. And a note on brands: manufacturer stability matters as much as headline price, because a battery is only as good as the warranty behind it. When you are ready, use the figures here as a sanity check, then get real quotes from vetted, MCS-registered installers so you can compare fitted prices and brands against your actual home.