That farm-gate milk price estimate was conservative and, if prices stayed at current levels, the price could go as high as $6.40, Penny said.
Westpac's forecast was 30c higher than Fonterra's current forecast and the difference reflected the dramatic price movements over the past two auctions which might not have been fully incorporated into the dairy co-operative's forecasts, he said.
With prices moving so fast, a wide range of final results were possible and auctions over the next three months or so would be critical in determining the final farm-gate milk price.
Westpac has also increased its forecast farm-gate milk price for the 2013/14 season by 30c to $6.20.
While the bank expected dairy prices to eventually settle at a lower level, underlying demand, particularly from China, remained strong, while global supply also remained constrained this year.
Milk production in the south had not been affected as much as in the drought-stricken North Island.
While revenue might be higher than last year costs would be up and production down in the North Island, while South Island revenue would be up and costs should largely be the same, Penny said.