About SunSums

Free calculators that answer one question honestly: what would this actually save my home?

Who runs it

I'm Tej. I live in the South East with solar panels, a Tesla Powerwall and an electric car, all on Octopus. Before buying I couldn't find a calculator that did the sums properly: half hour by half hour, with the real prices for my region, the cheap overnight window and what I'd be paid for export. So I built one, and SunSums grew from it.

I still run my own house on the same maths. When something here changes, it's usually because my own numbers taught me something.

How SunSums works things out

• Real prices. Octopus Energy's published prices for each of the 14 UK regions, including VAT and standing charges. Every page says the date its prices are from.
• Half-hourly maths. A typical day for each month is built half hour by half hour: what the house uses, when the sun shines, when the car charges, when the battery fills and empties.
• Your own data if you want. Upload your Octopus usage file to the Tariff Finder and every half hour you really used is priced. The file is read in your browser and never sent anywhere.
• The limits are written down. Each tool lists what it leaves out. These are estimates for planning, not quotes and not financial advice.

How SunSums pays for itself

There are no adverts and nothing is sold about you. Three things keep it going, and none of them changes a result:

• The Octopus referral link. If you join Octopus with it, you and SunSums each get £50 account credit. The calculators rank every tariff the same way whether or not you use the link, and they will happily tell you to stay where you are.
• The Playbook (£9, sold through Payhip): the settings and tricks that make a tariff pay.
• Buy me a drink: a one-off thank you, if a tool helped.

SunSums is independent. It isn't owned by, paid by or affiliated with Octopus Energy, Tesla or any installer, beyond the referral scheme any Octopus customer can join.

Corrections

If a price is out of date or a number looks wrong, please tell me at [email protected]. I fix mistakes quickly and say what changed.

Still on your cheapest tariff?

One short email at the start of each month: what changed in your region's Octopus prices, and which tariff is cheapest now for homes like yours. Free, no spam, one click to leave.

Your regionYour region…East EnglandEast MidlandsLondonMerseyside & North WalesWest MidlandsNorth EastNorth WestSouthern EnglandSouth EastSouth WalesSouth WestYorkshireSouth ScotlandNorth ScotlandYour emailSend me the check-up

You'll get one email to confirm first. Your address is kept by our email service, Buttondown, for SunSums only and never sold or shared. Privacy · What you get