Interim chief executive Derek Wright puts the blowout down to an increase in staff costs, population growth, acute hospital presentations, consumable costs "coupled with a challenging savings plan".
Wright said the DHB initially predicted it would break even at the start of the financial year.
"[The forecast] was then adjusted to a $10m deficit budget due to depreciation on revaluations of our buildings, but we are now halfway through the year and we are very unlikely to meet this."
The DHB had factored $39m of savings into a break-even budget, but although it had already achieved savings of $13.3m the remaining $26.7m was "going to be a struggle to fully achieve because of the complex nature of the savings initiatives and the lead time needed to deliver the benefits", Wright said.
"These include a theatre performance and productivity initiative, a patient-flow programme, an acute-demand management project and a wide range of smaller initiatives across the organisation."
The DHB at present had a $1.7m deficit budget.
Despite the debt, Wright said he was "confident that we are doing the right things" that would have big financial benefits.
"But it is just taking longer than we had hoped. We knew it was always going to be extremely challenging, and it has proved to be so."
Making it "particularly challenging" was the board's stance that the pursuit of savings should not affect access to services or the quality of service offered.
"Our latest forecast is a deficit of $21.8m on our overall budget of $1.4 billion and we have informed the ministry of this."
Keeping to budget was a struggle for most DHBs in the 2016/17 year, with only five of the 20 boards coming in under budget.
Canterbury DHB had the largest deficit - $51.8m.
In total the DHBs racked up a $117m deficit during the period, almost $60m more than was budgeted for.
In the 2015/16 year Waikato was one of eight DHBs to record a surplus above its annual approved budget.