From the BBC Economics Editor, John Campbell, Here is a brilliant cost analysis of just how the figures add up.
How does the £500m add up?
Most of the new money is dedicated to issues that are Northern Ireland specific.
A total of £188m will be made available for security-related spending.
The PSNI will get an unconditional £160m over the next five years to tackle dissident republicans and other paramilitaries.
A further £25m will be released if the executive comes up with matched funding from its own resources.
The remaining £3m relates to the cost of establishing a new monitoring and implementation body.
‘Shared future’ cross-community issues will benefit from an additional £60m over five years.
Some of this money will go towards projects aimed at leading to the removal of Belfast’s ‘peace walls’.
There will be £125m for the Social Security Agency to tackle fraud and error.
But here is where the final number becomes a bit less certain.
The assumption is that the investment will allow the Social Security Agency to detect up to £300m of additional fraud and error over the next five years.
Stormont will be allowed to keep half of that money.
In the last financial year, the Social Security Agency detected losses of £17.4m from official error, £9.3m from customer error and £25.2m in customer fraud.
That’s a total of £51.9m .
So the assumption is that the new investment will increase detection of fraud and error by more than 100% per year.
The politicians seem confident that is achievable but if it isn’t the financial package could come up short.
The other thing to bear in mind is that the DUP and Sinn Féin have decided they will fund measures to mitigate the impact of welfare reform.
Those mitigating measures will remove £585m from departmental spending – more than is being gained in this financial package.