Yes @WishyFishy. We've done the kilowatt per hour calculation based on our actual usage.
We are a firmly average use household. Our bills have tracked alongside the energy cap's average for a couple of years. When average cost was £1200 a year we were paying £100 a month.
Most of the last few years the price cap was about £1200, in April it went up to £1,971, but our direct debit didn't go up because we had a small surplus and the rise was only 25%. Yesterday it went up to £3,549, in January it's expected to be £5,386, and then go up to about £7k in April. More in October.
The average energy bill for the four weeks of January alone is expected to be £700 for an average user on dual fuel. Similar in February
I believe there is a very rough calculator on Martin Lewis's site, but it's only for today's rise, not January's and April's.
£250 a month might get you through the next three months but it's nowhere near enough for the next 12.