This is an interesting site, with a graph of debt back to 1970 and easily modifiable data sets:
http://usgovernmentspending.com/spending_chart_1970_2027USb_24s2li111mcny_H0t
We know we we are well past the point where ANY country has ever recovered, on a debt to GDP basis, but we also know Japan has been beyond way beyond that point for probably 3 decades now and still hasn't gone full Zimbabwe.
We also know that we are way past the point where additional debt actually grows the economy. We are now into a tail wagging the dog phase, where NOT continuing to Ponzi at an accelerating rate causes implosion into a black hole.
We were overdue to switch to a new "system" of monetary fraud around 2003. I was quite surprised 2008 wasn't a lot worse than it was, as we actually didn't fix anything - but arguably only made the problem vastly worse and impossible to predict.
I think backing new money issuance with supposed "interest" is way past its expiry date. I expect the government to stop pretending to be "borrowing" and just start printing nakedly. Maybe they should just print $31 trillion+5%($31 Trillion) and pay off all the debt + current interest? Hmmm. So $31 Trillion at 5% is about 1.5Trillion INTEREST ALONE PER YEAR on existent debt.
http://cnsnews.com/article/washington/terence-p-jeffrey/4896119000000-federal-tax-collections-set-record-fiscal-2022. Hmm. Almost $5Trillion, so more than I expected - we are only WASTING 30% of "our" income per year on "credit card" interest! ;-).
By 2025, we should be well above 50% on your extrapolation, it seems reasonable (almost inevitable) say?
Can you imagine how exciting it is going to be living in the US, "Land of the Free and Home of the Brave", on - say - a government pension with medicare?
We need to keep digging on your chart! Finding a reasonable imputed compounding factor would allow us to be much more certain of timeline!