How to file UK tax where US and UK use Different Tax Years

I am an American pensioner married to a UK Citizen (so I'm a non-dom UK resident).  I am filing a self-assessment in the UK, using the arising basis (for the first time).  My question is, which US tax year/return do I use to report my US income to HMRC?  I have no way to split it into UK tax years.

Thanks

I am an American pensioner married to a UK Citizen (so I'm a non-dom UK resident).  I am filing a self-assessment in the UK, using the arising basis (for the first time).  My question is, which US tax year/return do I use to report my US income to HMRC?  I have no way to split it into UK tax years.

Thanks

You just have to keep good records. If you had a W-2 for 2011 and you were filing in the UK for 6th April 2011 through 5th April 2012 I'd pro-rate your US taxes and income for 2011 and add on the income and tax you paid up to 5th April 2011

That makes sense.  If I took 9/12 from my 2011 W2 andd 3/12 from my 2012 W2, then should I calculate the exchange rate for each piece as of April of each year?

Thanks for your suggestions