The means test for Rent Supplement is different than that for One Parent Family. You will be disqualified if you work more than 30 hours per week as that is considered fulltime work.
If you work less than 30 hours, the re-assessment will be based on your wages and your One Parent Family Payment.
Your additional household income (the amount of income above the SWA rate for your family size) will be assessed as follows:
The first €75 is not taken into account. Also, 25% of income over €75 is not taken into account. There is no upper limit on the amount that can be disregarded.
The SWA rate is currently 204.30 for an adult plus 26 euro for each child.
Income is calculated as your gross wages less PRSI.
It can be a complicated calculation, especially if your One Parent Family payment changes, but you might get some idea of your ongoing entitlement from the above.