Fortescue Metals Group shareholders could be in line for an even bigger than expected dividend windfall after the company revealed it made a $US950 million net profit in December alone on the back of high iron ore prices.

Chairman and founder Andrew Forrest let the cat out of the bag on the December profit during the pre-recording of the first of his Boyer lecture series for the ABC due to air on Saturday.

Fortescue issued a profit update on Friday, saying it expect first half NPAT of $US4 billion to $US4.1 billion. It is due to release first half results on February 18 along with details of a first half dividend.

The iron producer’s share price had dipped about 1.6 per cent to $24.46 late on Friday as BHP and Rio Tinto also lost a little ground.

The UBS estimate for Fortescue’s first half NPAT was $US4.18 billion and consensus forecasts $US3.95 billion.

Shaw & Partners analyst Peter O’Connor said forecasts for the full year were running at about $US7.2 billion based on a first half number close to $US4 billion, but the December figure might prompt a re-think.

Read more about Fortescue's profit update here.