S&P Global Ratings downgraded Kiwibank's long-term issuer credit rating to A from A+ after the bank's unconditional guarantee from majority owner New Zealand Post expired.
The agency also affirmed its short-term issuer credit rating of A-1 and the A+ rating on the outstanding long-term debt issued by Kiwibank during the guarantee period.
"Our long-term issuer credit rating on Kiwibank now incorporates three notches of uplift above the bank's stand-alone credit profile. Previously, we incorporated a four-notch uplift above the bank's SACP resulting from the guarantee from NZ Post," said S&P credit analyst Andrew Mayes.
"The current rating reflects our assessment that the bank is highly likely to receive extraordinary support from the New Zealand government, if needed. This is because we consider that Kiwibank plays an important role to the New Zealand government and that the bank has a very strong link to the government as a result of its indirect ownership by the government."
S&P's outlook for Kiwibank is stable, reflecting its expectation the bank will retain its focus on relatively lower-risk residential lending while maintaining its risk-adjusted capital ratio above 10 per cent.