The figure of £10b, frequently quoted as representing the UK government annual subvention to Northern Ireland, is a UK accounting exercise. The total includes central UK government costs allocated to Northern Ireland that would not be relevant to a United Ireland. This article analyses the most significant elements of the subvention - pensions, UK national debt repayments, defence expenditure, other non-identified expenditure, and under-estimates of Northern Ireland’s share of UK tax revenues. It concludes that those elements of the current subvention that are likely to transfer to a united Ireland, would represent a deficit of approximately €2.8b. As existing economic models of an all-island economy, predict a positive impact on economic growth, at a level sufficient to cover this deficit the economic debate on Irish unity needs to move on from a discussion of the subvention. The debate now needs to focus on the public policy decisions necessary to support sustainable economic growth and to maximise the benefits of a larger and integrated all-island economy. The underlying economy, taxation system and the type of public services that are provided in health, welfare, education and infrastructure, will be the real issues that will shape the costs and benefits of a united Ireland.