Enegy usage between 23 August and 5th February - how to know what Itl roughly be across the year?

[NemophilistRebel]

My later energy bill has come for the last 5 and a bit months over winter

The costs of usage taken from meter readings is £645

Can anyone give a rough idea how I can then guess at what it would be for the next 5 months which will be partly spring and summer?

Well a rough idea will be 'about the same'.

Depending on where you are in the country, up to now, winter has been exceptionally mild, and there's still at least two months where it could be considerably colder, so the heating bill could well be higher.

The period you say covers about 5 and a half months. The next 5 and a half months takes us until late in July, but it very much depends on the weather during that period.

Assuming you're in the UK, the time of year only has the vaguest correlation as to the external temperature and I remember as many cold wet Junes and Augusts as I do mild, warm and sunny Aprils, Mays Septembers and Octobers.