If you’re on Octopus Intelligent Go or thinking about switching to a smart EV tariff, you’ve probably heard rumblings about something called Market-wide Half-Hourly Settlement (MHHS). It sounds boring, but it matters. From late 2026, this change could affect how much you pay to charge your car overnight, and whether those brilliant 7p per kWh rates remain quite so brilliant.
Here’s what’s actually happening, what it means for your charging costs, and whether you need to do anything about it.
What Is Half-Hourly Settlement?
Right now, most domestic electricity meters are read monthly or quarterly, and your supplier estimates your usage patterns based on broad assumptions. They might know you used 300 kWh this month, but they don’t necessarily know exactly when you used it.
MHHS changes this. By late 2026, all domestic meters in Great Britain will report your electricity usage in half-hourly chunks. Your supplier will know precisely when you’re using power, which means they can charge you based on what electricity actually costs at different times of day, rather than averaging it out.
Think of it like switching from a monthly phone contract with unlimited data to a more detailed plan where you can see exactly how much data you used each day. More information, more accuracy, potentially better deals if you’re clever about when you use things.
How This Affects Octopus Intelligent Go
Intelligent Go currently offers 7.5p per kWh between 11:30pm and 5:30am (at the time of writing), with a higher day rate around 24p per kWh. It’s a flat rate during those hours. You plug in, the app tells your car when to charge, and you pay the same price whether it’s midnight or 4am.
Under half-hourly pricing, those overnight rates could vary within that six-hour window. Some half-hour periods might be cheaper than 7.5p when demand is rock bottom and wind generation is high. Others might be slightly more expensive.
The good news is that Octopus has consistently said they’re keen to pass wholesale price benefits onto customers. If electricity is genuinely cheaper at 3am than at midnight, there’s a good chance you’ll see that reflected in your bill. The smart charging system will simply shift your car’s charging to the absolute cheapest slots available.
Will You Actually Pay More?
Probably not, if you’re using smart charging properly. Here’s why.
The wholesale electricity market already operates on half-hourly pricing. Energy suppliers buy electricity in half-hourly blocks, and prices absolutely plummet overnight when demand drops. What MHHS does is let suppliers pass those specific prices directly to you, rather than averaging them out.
If you’re charging at the genuinely cheapest times (typically between 2am and 4am), you might actually pay less than you do now. If you’re charging at the edges of the cheap period, say at 11:30pm when demand is still relatively high, you might pay a bit more than the flat 7.5p rate.
The crucial bit is that smart charging apps like Octopus Intelligent will automatically optimise for this. They’ll schedule your charging during the absolute cheapest half-hour periods within the available window. You won’t need to faff about with spreadsheets working out when to plug in.
What About Other Smart Tariffs?
This affects all smart tariffs, not just Intelligent Go. OVO’s Charge Anytime, for instance, already uses dynamic pricing behind the scenes to schedule your charging. That model actually fits quite neatly with half-hourly settlement.
Simple time-of-use tariffs like Octopus Go (the non-intelligent version) or EDF’s GoElectric might need to evolve. They currently offer a flat cheap rate for a set period. Under MHHS, they could either introduce more granular pricing or maintain flat rates but adjust them more frequently based on market conditions.
Should You Change Your Charging Habits?
Not really. If you’re already using smart charging, carry on. The app will handle the optimisation.
If you’re manually setting your car to charge at a specific time, you might want to reconsider and let the app do its thing. When prices vary within the overnight period, having the flexibility to charge whenever it’s cheapest matters more than it does now.
One practical tip: make sure you’re giving your smart charging app enough flexibility. If you tell it you absolutely must have a full battery by 6am every day, it might need to charge during slightly more expensive periods to guarantee that. If you can be more relaxed, say you only need 80% most days, the app has more room to wait for the cheapest slots.
The Honest Assessment
MHHS isn’t something to panic about. For EV drivers using smart charging, it’s likely to be neutral or slightly beneficial. You’re already charging at night when electricity is cheap. This change just makes that pricing more accurate and potentially rewards you for being even more flexible.
The people who might struggle are those who can’t shift their electricity usage to off-peak times, or those without smart meters who’ll face higher standing charges to cover the cost of manual meter reads. But if you’re charging an EV overnight, you’re already doing exactly what this system is designed to encourage.
Keep an eye on your tariff provider’s communications as we get closer to late 2026, but there’s no need to switch suppliers or change your routine now. The fundamentals remain the same: charging overnight will still be much cheaper than charging during the day, and smart charging will still save you money.