Self Employed. What are my Earnings?

[ManyQuestions]

Hi, I have considerable savings which I would now like to start paying into a SIPP. I understand that I can pay in up to my earnings to get tax relief, and I know that the earnings figure excludes investment income and rent. Here is my question: I am self employed. I calculate my earnings when I prepare accounts, so the number might not be clear until a year or more after the mount is actually earned. This figure goes up and down significantly from year to year. So what figure do I use to decide how much I can pay into a SIPP in any paticular year and be able to claim tax relief?
Thanks

[pawncob]

I believe you can contribute to a SIPP historically, so you can top up your contribution when the results are known.

[jason13]

I believe you can contribute to a SIPP historically, so you can top up your contribution when the results are known.

No, you can only make contributions for the current year.