Compiled for Asda by London economists CEBR, the latest income tracker shows families in the region have an extra £8 a week compared with a year ago.
However, their discretionary income of £103 a week compares with a record UK average of £201.
Discretionary income is money left over after tax and bills and expenses, like a mortgage and food spending, are paid.
According to the quarterly income tracker report, the situation in Northern Ireland reflects lower rates of pay compared with other regions of the UK.
Additionally, it says almost 10% of Northern Ireland workers in 2014 were employed at or below the minimum wage compared with just over 5% across the UK as a whole.
Wales has discretionary income of £180 a week, Scotland has £200, and the poorest English region, the north-east, has £133.
The pace of growth has slowed considerably for Northern Ireland householders - it rose by 9% between April and June, compared with 18% in the corresponding quarter of 2015.
Household spending power in Northern Ireland is about half the UK average, according to new data.