Many West Australian wheat farmers may not turn a profit this year, with wheat prices falling to a five year low.

The price of wheat has plunged from a record $430 to only $220 a tonne, in the past 18 months.

Commodities analyst, Tony Smith, has attributed the fall to a global over-supply of wheat and the strong Australian dollar.

Mr Smith says farmers have also had to pay close to record prices for fertiliser and fuel, further eroding any profits.

"So they've actually come off a year where they've paid a significant amount for their inputs, so you'd actually say at these sort of levels, that most farmers unless they get above yields will be losing money this year," he said.

The Agriculture Department is predicting a bumper 12 million tonne harvest this season, with eight million tonnes of wheat.