Back of napkin calculations to make UBI work in US:

First, you start with non-institutionalized adult citizens that brings you down to a payee base of ~210M (this part will be unpopular as parents will want to get more than other adults).

Next you set the basic income at the poverty level for a single person, $11,700. That gives you a total nominal cost of $2.47T.

You do not exempt the basic income from the normal taxation rules. That means you get some of it back in taxes. If you figure 20% that gives you a net cost of $1.97T.

You then take a buzz saw to all social spending aimed at US citizens, including all parts of social security (this would be very unpopular among the elderly, near elderly and disabled). With all parts of social security adding to more than $800B/year It's fairly easy to find a $1T in savings there. That brings the total to under a trillion dollars.

You take a buzz saw to tax expenditures, e.g. exclusion of fringe benefits, preferential rates for capital gains and dividends, mortgage interest deduction, state and local tax deduction, etc. (this is also going to be very unpopular). If you add it up, that's good for another $550B.

That leaves you with another $420B in new non-offset spending. I'm certainly not going to to claim that's a small number, but it seems achievable. It's about 2.3% of GDP. Maybe you can get states to kick in (or force them to through reduced grants in aid) given that some of their social programs can also be largely reduced or eliminated.

From https://news.ycombinator.com/item?id=10172076

So for UBI to work, you have to antagonize parents (no baby/child/family bonuses), seniors (they'll be worse off than they would be with pension + medicare), the middle class (tax deductions evaporate), the wealthy (capital gains/dividend tax overhaul) and the whole populace through the tax hike required to cover the remainder of expenditure (the 2-3% GDP gap). Who wins in this scenario? The poor, unemployed, students == approx the same beneficiaries of the supremely unpopular and soon to be repealed Affordable Care Act.

Back to the drawing board.