Reporting UK self employment taxes on US returns

I file self assessment taxes in the UK because I have a tiny freelance business. Last year I finally made enough money to owe taxes to the UK on this, but I'm not sure how to report it on my US tax return because the fiscal years don't line up.

To simplify, I had to pay £175 in tax on top of what was withheld from the paychecks from my regular job. But this is for the period April 2015 - April 2016 rather than January - December 2016. Figuring the income for the calendar year is easy but how do I do the tax?

Can I just work out what percentage of the taxable income was from 2016 and report that same percentage of the tax paid on my US returns?

US law lets you claim a foreign tax credit on the cash basis. You claim a credit for foreign tax paid in the calendar year. If you delayed paying this to HMRC until 2017 you will claim credit on your 2017 return.