Octopus Cosy is structured differently from most EV/off-peak tariffs, and that difference specifically favours heat pump owners more than most other tariffs do. Where a typical two-rate tariff offers one cheap window overnight, Cosy has three cheap windows every day — 04:00–07:00, 13:00–16:00 and 22:00–00:00 — plus an evening peak from 16:00 to 19:00 priced above its standard rate. The midday window is timed to line up with when heat pumps run most efficiently (milder outdoor temperatures) and, usefully, with when solar panels are generating.
What makes Cosy's structure different
Most off-peak/EV tariffs give you one cheap overnight window and a single higher rate for the rest of the day. Cosy has three rates instead: cheap in its three windows, a standard rate for most of the day, and a higher peak rate from 16:00 to 19:00.
Current rates for Cosy, from Octopus's published tariff data: 12.4p–13.8p per kWh in the three cheap windows, 25.3p–28.0p per kWh at the standard rate and 38.0p–42.0p per kWh in the 16:00–19:00 peak. The range is across Octopus's 14 regions (direct debit, including VAT), checked 27 September 2026.
That changes several of the standard calculations this site's other guides walk through:
- Heat pump scheduling: running assumptions built for a single overnight cheap window don't fit Cosy. A heat pump can run a meaningful share of its hours in the three cheap windows — including 13:00–16:00, when outdoor temperatures are milder — and avoid the 16:00–19:00 peak, improving the running-cost comparison against gas.
- Solar and battery interaction: the 13:00–16:00 window overlaps with typical solar generation, so solar you use yourself then displaces cheap electricity rather than standard-rate electricity — it's worth less in those hours than at other times of day. That changes the export-vs-divert comparison covered in our diversion method guide, so re-run it with Cosy's actual rates rather than assuming a generic two-rate result applies. A battery can also fill up in the cheap windows and cover the 16:00–19:00 peak.
What to check before assuming Cosy is right for you
- Your own rate and windows — the rates above update daily from Octopus's published data, but the rate you'd pay depends on your region, and Octopus can change the windows; confirm both on your quote.
- Whether your usage pattern actually benefits — Cosy's advantage is specifically for heat pump and flexible-usage households. A household with minimal daytime flexibility gets less benefit from the midday window than the headline structure suggests.
Want a guide to how your own home looks on Cosy, across solar, battery and heat pump together? Our free calculator has a Cosy option: pick it on the first step, enter your three rates, and it prices solar self-use, battery charging, EV charging and heat pump running by the Cosy window each one falls in.