That is a good question and I was thinking about it today. I would have presumed the opposite to you i.e. if you pay the social insurance charge on your income you would be entitled to the benefits.PRSI is an insurance you pay to provide you with benefits, right? So if I get charged prsi on my deposit interest what benefits do I get? Presumably this is not counted as a contribution for the purposes of going toward pension benefits for example assuming I have no other taxable source of income and not getting a prsi contribution any other way.
However as a PAYE worker with no investment income (other than deposit interest) and to whom Form 12s, Form 11s etc. are alien, I find this issue confusing.
I would also be interested to see what happens for pre and post 1995 public servants. What rate of PRSI would the pre 95ers pay on their deposit interest, if it is full PRSI could they then become entitled to optical and dental benefit and get a contributory old age pension on top of their public service pension resulting in a combined pension of greater than half their final salary.
If, as speculated by several posters in this thread, PRSI will not be payable on States Savings interest, would a post 1995 public servant be better off with State Savings. They will receive no extra benefits from paying PRSI on deposit interest so they might as well put their savings into a product that is (possibly) PRSI exempt.