Calculate your savings
Best case: one full cycle a day, all used at the day rate, assumed 90% round-trip efficiency (formula: capacity × day − capacity/0.9 × night, × 365). Real savings will be lower. Octopus Go rates checked 10 October 2026 (GO-FIX-12M-26-09-29). See how we worked it out.
How the savings calculation works
The savings from a home battery come from charging overnight at the cheap rate and using that energy during the day instead of buying at the daytime rate. We assume 90% round-trip efficiency, so to deliver 5 kWh at the day rate you buy 5 ÷ 0.9 kWh at the night rate. Here is the formula:
Example (5 kWh on Octopus Go in Yorkshire, checked 10 October 2026):
5 kWh × 33.555p − (5 ÷ 0.9) kWh × 9.5p = 114.9972p saved per day
114.9972p × 365 = £419.74/year, best case (about £420)
Across UK regions the best-case range is about £420 to £490 a year. Best-case payback on £2,499 is about 5.1 to 6.0 years. See how we worked it out.
Savings comparison by tariff (5 kWh, best case)
Figures below use the same formula as the calculator. Octopus Go day rates vary by region (33.555p to 37.4209p, GO-FIX-12M-26-09-29, checked 10 October 2026). Intelligent Octopus Go has a 7.6p off-peak rate for 6 hours (23:30 to 05:30) for your home (Octopus Energy). Octopus quotes its day rate per home, so we do not show one here: pick Intelligent Octopus Go above and enter the day rate from your own quote.
| Tariff | Night | Day | Best-case annual (5 kWh) | Best-case payback on £2,499 |
|---|---|---|---|---|
| Octopus Go (Yorkshire to North Wales) | 9.5p | 33.555p to 37.4209p | about £420 to £490 | about 5.1 to 6.0 years |
| Intelligent Octopus Go (requires EV) | 7.6p (6 hours, 23:30 to 05:30) | Your quoted day rate | Enter your day rate in the calculator | Depends on your day rate |
What about payback?
Your payback period is the cost of your battery system divided by your annual savings. For Habo's 5 kWh EcoFlow STREAM from £2,499 on Octopus Go, best-case payback is about 5.1 to 6.0 years (see the maths). Real savings will be lower, so real payback is longer.
Factors that affect your savings
Your tariff spread is the biggest factor. A bigger gap between off-peak and peak rates means more savings. On a flat-rate tariff with no off-peak period, a standalone battery saves nothing.
Battery size determines how much energy you can shift per day. A 10kWh battery shifts roughly twice as much as a 5kWh - and saves roughly twice as much.
Your actual usage matters too. If you use less electricity during peak hours than your battery can supply, the excess capacity goes unused. A battery matched to your peak-hour consumption delivers the best returns.
Round-trip efficiency (the energy lost during charging and discharging) varies from battery to battery. Our calculator assumes 90%.
Like what you see?
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