ANZ has the lowest payout ratio of the big four. NAB has the...

ANZ has the lowest payout ratio of the big four. NAB has the highest. ANZ is paying out about 68% of earnings as dividends. NAB is paying out about 85% of earnings as dividends. NAB is therefor retaining less earnings than the other big four. NAB has to do some work to achieve the tier 2 capital requirements of the regulator. Investors may be nervous about slowing loan growth (especially housing) plus pressures on lending margins (overseas sources of borrowings are getting more expensive due to rising US interest rates). Additionally, there may be risks associated with whatever regulatory tightening and associated compliance costs, plus any further financial penalties/recompence arising as a result of the current Royal Commission.

If an investor has a negative outlook on the profitability of banks, NAB would be considered the most exposed to risks of lower earnings. In other words, NAB's dividend might be considered the least sustainable of the big four in any downturn in bank earnings and profits.