The new European Citizens' Initiative for Unconditional Basic Income has been launched. It will be examined by the commission if one million citizens support it, so I invite you to sign it and share it: https://eci.ec.europa.eu/014/public/#/screen/home
In terms of maths, it depends on the implementation.
UBI is no different from social benefits that almost all countries have except that they're mostly conditional (for child, for unemployed, for homeless etc) while UBI is simply unconditional, granted to everyone.
Then UBI can be compared against tax free income, or income threshold for which you don't pay income tax, that is universal except it only applies to people who earn money from employment.
Also worth adding that in terms of general "why benefits" there was a significant discussion among early economists on that subject back in 19th century. One of the most systematic voices on that topic was... Adam Smith, who is today associated with laissez-faire market - incorrectly, and mostly by under-educated neoliberals. In his "Inquiry ..." he lays ideas that today would be probably classified as "socialism", especially in the US. http://www.gutenberg.org/files/3300/3300-h/3300-h.htm#chap35
The power of capitalism lies in its flexibility and "whatever works" pragmatism. If you start artificially limiting what is allowed and what is not then it's not, then it loses this pragmatic approach at the cost of dogmatism. Smith specifically did not come up with his ideas for public schooling (as an example) from ideological position, but he built an evidence-based argument for it.