The research found that mental stimulation, a sense of purpose and being in good health were popular reasons why 398 doctors - out of 1018 doctors surveyed aged 55 or older - stated they either did not intend to retire, or were not sure about it.

The study found that among the 650 doctors intending to retire, the top factors stated as affecting the timing were: wanting more leisure time, financial security, physical illness or disability, and cognitive impairment.

Royal Australian College of General Practitioners president Bastian Seidel said the study was important.

He said it belied claims by health workforce agencies and medical schools that we face a glut of GPs retiring over the next few years, and that therefore we should increase our overseas-trained doctor intake and boost medical school numbers.

The study, conducted by Flinders University, the University of NSW and the University of Sydney, is published in the Medical Journal of Australia on Monday.

It is based on an online questionnaire, carried out in October, 2015, of currently practising Australian doctors aged 55 or older.

Of the total respondents, 62 per cent said they intended to retire, 11.4 per cent had no intention of retiring, and 26.6 per cent were unsure.

Among the 398 doctors who stated they did not intend to retire, or were not sure about it, a high number (87.7 per cent) said they strongly agreed or agreed that the cognitive stimulation of being a doctor was an important factor.

Other strong factors were a sense of purpose or goals (80.9 per cent), being in good physical health (78.4 per cent) and maintaining fulfilling professional relationships (63.8 per cent).

When the 650 doctors intending to retire were asked what factors would affect the timing, more than two in three (67.4 per cent) cited "desire more personal leisure time".

Also in this group, 57.1 per cent stated "financial security", 56 per cent named physical illness or disability and 54.5 per cent cited cognitive impairment".

And 34.6 per cent cited the ability to access superannuation.

Dr Seidel said: "It turns out that older GPs are not retiring after all."

He said the reasons were financial, with the Global Financial Crisis causing a significant drop in retirement savings.

"The average GP income is now $130,000 (female), $180,000 (male) i.e. less than half of what a hospital doctor would earn. So to make up for the funding shortfall, GPs work longer."

Dr Seidel, 41, a GP, said he had recently changed his income protection insurance so he is covered until age 70, not the standard 65, "as I can't see myself retiring any time soon. That certainly is the sentiment amongst Gen X GPs, plainly because of the limited income potential in General Practice."