Too many university applicants realise too late they picked the wrong school subjects at 16, says Which?
The consumer group said almost a third (28%) of more than 1,000 UK 18- and 19-year-olds university applicants surveyed said they wished they had chosen different subjects.
And 41% wished they had considered which subjects would be of most use.
The Russell Group of selective universities said clear information on subject choice was crucial.
The research, carried out by Youth Sight, in January, also found only about half of the university applicants felt well enough informed at school about how the subjects they had studied could affect their choice of degree and university.
Some degrees require specific A-levels of equivalents and some universities do not consider certain subjects challenging enough, warns Which?
However, only 41% of the teenagers surveyed were aware of this.
And 30% complained the advice they had received had failed to warn them of the impact choices made at 16 could have on their future prospects.
Russell Group director general Wendy Piatt said it was "really important for all young people, especially those whose parents didn't go to university, to have clear information about how the subjects that they choose to study in the sixth form or at college can affect their options at university and their chances in life".
In 2011, the group published its Informed Choices guide to the most useful school subjects for students aiming at one of its 24 universities.
The guide suggests 16-year-olds should study two of the following "facilitating" subjects to keep a wide range of options open:
- English literature
- modern and classical languages
- maths and further maths
Which? University has also launched an Explorer tool to help 16-year-olds and their teachers to explore their options.
"While certain A-levels might suggest a particular degree path, our tool shows there are usually alternative options students can take," said Which? campaigns director Alex Neill.
And student Dan French, who is applying to Salford University, said he wished it had been available when he had been 16.