Despite funding increasing by an estimated pound;72 million, the survey of about a third of all colleges found that most would receive less per student, as the numbers rise by at least 22,000 above this year's record recruitment.
It equates to an average 0.5 per cent reduction in funding for each 16- to 18-year-old, which colleges say will mean they have to offer more restricted programmes.
One sixth-form college principal's response in the survey was that constraints on funding meant that the "international baccalaureate is dead in the water".
Julian Gravatt, assistant chief executive of the AoC, said: "Colleges will take a long, hard look at courses that are expensive now."
But the picture is not uniform. Just under a third of colleges will receive a cut in funding in absolute terms, while about one in eight will receive large increases of more than 10 per cent, reflecting greater predicted recruitment at large general further education and land-based colleges. There are also regional variations, with the figures suggesting that colleges in the North East will lose 1 per cent of their students while in the South East numbers rise by 0.7 per cent.
The AoC said an extra 11,000 student places yet to be allocated could counterbalance this if they are distributed according to the numbers out of education or training.
Colleges said it was hard to justify reducing their allocations because of new school or academy sixth forms. In the case of academies, they are recruiting 2,000 fewer students than expected, despite record numbers in the system as a whole.