The increase in rates is identified by Duncan as the biggest challenge of the council's current term.
"We were again faced with the near impossible balance between cutting back as much as possible to reduce rates for those on fixed and low incomes, and knowing that we need to grow the number of properties to spread rates and to do that Whanganui needs to be vibrant and attractive."
Rates increased an average of 3.7 per cent for the 2019/20 year, up 0.2 per cent on that previously identified in the Long-Term Plan.
Duncan said it's an area of the council's business she would like changed.
"I'd like to be able to affect change to the rating system which in my view is well past its effective use-by date."
After two terms on the Whanganui District Health Board, Duncan has decided she won't stand for the position in this year's election.
"If we're going to improve health outcomes we need to do that by changing environments and behavior, and I'm more able to influence that through council.
"I'm looking forward to being more focused rather spread thin as I have been in the last few years."
Some of the Deputy Mayor's other roles include acting chairwoman of the Audit and Risk Committee, chairwoman of the Chief Executive Review Committee, and co-chair of Te Rūnanga O Tupoho working party.