Renouncing my US citizenship

Hi,
I'm a dual US/UK citizen although only as an accident of birth. I was a six week on old baby when my British parents returned from the US back in the early 1970's and i've spent the last 44 years living in the UK. Naturally I don't consider myself to be American.
In the mid 1990's I got a US passport because the embassy told me I had to in order to visit the US. I've been doing tax returns since 1996 and I think i'm all correct and up to date.

However the stress of the US tax system is wearing on me and i'm considering renouncing.

I've been reviewing form 8854 and have a question about my 'Income Tax Liability'. It isn't immediately obvious to me what this is.

There is a good article on Hodges Law which concludes that you use line 55 of your 1040. Can anybody confirm this? It seems a bit of a minefield.

newcomer link: http://hodgen.com/how-to-compute-net-tax-liability-for-form-8854/# [nonactive]

Sorry if this is the wrong forum to ask.

Line 55 on the 2012 form. The line numbers aren't necessarily the same from one year to the next.   

PS There's a pointer to useful IRS guidance on the tax liability test and the net worth test in IRS Notice 2009-85 (https://www.irs.gov/irb/2009-45_IRB/ar10.html#d0e243)

B. Tax Liability and Net Worth Tests

For guidance on determining whether an individual is a covered expatriate by reason of the tax liability test or the net worth test, see Section III of Notice 97-19, 1997-1 C.B. 394.

Thanks Iota, looks like a useful link.

Tax liability is how much tax you owe...so just average that for 5 years.

For 2012 your tax liability is on line 55.....for 2015 it is on line 56.