GPs are to start predicting whether a patient has the early symptoms of cancer using a computer program that calculates risk, under plans to prevent the 10,000 unnecessary deaths a year caused by late diagnosis.

The new approach by the NHS means that doctors will tell patients their percentage chance of having cancer, based on factors like their age, weight and symptoms such as bleeding or sudden weight loss.

Professor Mike Richards, the government's cancer tsar, who unveiled the move in an interview with the Guardian, said that within five years every GP in England should be using the software as part of a new drive to reduce the huge toll of avoidable cancer deaths.

Computer-assisted cancer risk assessment will help GPs estimate whether a patient's symptoms could indicate the presence of a cancer and decide whether they needed to refer them for urgent tests in hospital, Richards said.

The computer would assess a patient's age, weight and symptoms – such as rectal bleeding and constant fatigue – and if the risk were above a certain level, the person would be referred to hospital for urgent exploratory tests within two weeks.

Cancer is the UK's biggest killer after heart disease and strokes. Every year 293,000 people are diagnosed with cancer, and about 155,000 die of it. GPs are vital because they spot the signs of cancer in 90% of patients, with screening picking up the other 10%. But a typical GP sees only eight or nine cases of cancer a year.

Britain is far worse than many European countries at diagnosing cancer early, when it is more likely to be treatable and the patient has a much better chance of surviving. That is partly because some patients who develop symptoms delay seeking help, but also because GPs sometimes fail to correctly identify signs of cancer.

Support technology is needed because of that poor record, the difficulty of diagnosing cancer and the sheer number of other ailments that GPs have to know about, Richards said.

There are more than 200 forms of cancer, and many of their symptoms are the same as for a range of other, often less serious, conditions. Computers could help doctors get it right more often when deciding whether to investigate a patient further, discharge them or refer them to hospital.

"This is helping GPs because none of us can retain this sort of information [about cancer symptoms] and having to retain it for bowel cancer, lung cancer and ovarian cancer, as well as for heart disease, it would take a remarkable human brain to be able to do that, so why not get computers to support it?" said Richards.

"The benefit of this will be that GPs will know who should be investigated and who shouldn't. It will also help patients to know that whether they are being reassured, or referred, or getting a test, that is the right thing to do."

Richards said the system would mean "better decision-making by GPs, leading also to earlier diagnosis of cancer patients".

Professor Steve Field, chairman of the Royal College of General Practitioners, welcomed the move. "The future of medicine will be that GPs will be using more and more computer-aided diagnostic tools for more and more conditions, and ultimately in years to come genetic information will be part of that," he said.

"GPs will welcome this because it will make their diagnoses quicker and better. Over time this will save lives."

Family doctors rather than computers will continue to make the key judgments, even after software has become routine in surgeries, Richards emphasised.

"The GP will always have the final say. If he wants to refer a patient to hospital, he will always have the right to do so," he said.

England is understood to be the first country in the world to move to introduce such technology, according to the Department of Health. A number of GP practices across the country will take part in a pilot programme to assess the effectiveness of assisted cancer risk assessment, starting in the spring. GPs have recently begun using similar software to help them assess a patient's risk of developing cardiovascular disease. It analyses blood pressure, family history, cholesterol, smoking history and current symptoms before producing an odds ratio.

The plan to extend the approach to cancer is underpinned by a series of recent DH-funded research studies by Dr Willie Hamilton, an Exeter GP and expert in cancer diagnosis at Bristol University. Richards said the tests had shown, for example, that a man aged over 40 who develops diarrhoea has less than a 1% chance of that indicating bowel cancer, but two visits to the GP with the same symptom produce a 1.5% risk. This rises to 3.4% if there is a combination of diarrhoea and rectal bleeding and 6.8% if he visits his GP twice with rectal bleeding.

Lord Naren Patel, the chairman of the NHS's National Patient Safety Agency, said: "This is a very good idea, to try to improve the early diagnosis of cancer, because we know that when cancers are diagnosed early that extends a patient's survival."

Sarah Woolnough, head of policy at Cancer Research UK, said: "We welcome any initiative that encourages the earlier diagnosis of cancer. Late diagnosis is the reason behind thousands of avoidable cancer deaths every year so it has to be a huge priority to make every effort to diagnose cancer earlier. We need to think imaginatively and innovatively about how we encourage earlier diagnosis, so initiatives like this are very promising for the future."