If you have HIV it is only natural to want to know what effect the virus will have on your health in the future and your life-expectancy.

The word used to forecast the likely course of a disease is 'prognosis'. It comes from an ancient Greek word that means ‘to know beforehand’.

The following factors affect the life-expectancy of people with HIV:

• CD4 cell count. This gives a rough guide to the health of the immune system.
• Viral load. The amount of HIV in the blood.
• Age.
• Developing serious illness because of HIV before HIV treatment is started.
• Infection with hepatitis B virus or hepatitis C virus.
• Injecting drug use.

Most HIV doctors are now hopeful that the right treatment and care can mean that a person with HIV in the UK will live a more or less normal lifespan.

Researchers calculated in 2008 that modern HIV treatment would mean that many people with HIV will be able to live well into their 70s.

There is growing agreement  that most people with HIV in the UK will die with HIV not of HIV.

The simple answer is that potent HIV treatment became available. The amount of illness and death caused by HIV has fallen dramatically since powerful combinations of anti-HIV drugs became available in 1996.

Doctors are also skilled at treating the infections that people with HIV can be vulnerable to.

HIV treatment doesn’t cure HIV, but it does stop the virus from reproducing and lowers amounts of HIV (viral load)  in the blood to very low levels. This allows the immune system to stay strong and fight infections.

It is recommended that everybody who is ill because of HIV should take HIV treatment. It is also recommended that you start taking HIV treatment when your CD4 cell count falls to around 350.

Taking HIV treatment before the virus has done too much damage to your immune system has also been shown to reduce the risk of heart, kidney and liver disease.

But some illnesses still occur more frequently in people with HIV.

Some cancers occur more frequently in people with HIV. These are often linked to infections. For example, people with HIV have higher rates of anal and cervical cancer and this is linked to infection with human papillomavirus (HPV), which is also associated with genital warts. Rates of mouth and throat cancer are also higher in people with HIV and could also be connected to HPV.

But it's important to note that these cancers are rare.

Many people with HIV are infected with hepatitis B virus and/or hepatitis C virus. These viruses affect the liver and can cause serious illness, even death.

Anti-HIV drugs can cause long-term side-effects and some drugs have been linked to an increased risk of heart,  kidney or liver disease.

It’s also important to note that about 400 people a year still die because of HIV in the UK. But the main reason for this is that these people had their HIV diagnosed late when they were already very ill because of HIV. They were not able to benefit from HIV treatment.

There is a lot you can do to look after your health and to give yourself the best chance of living a long and healthy life.

This includes:

• Making sure that you go to your HIV clinic for regular check-ups.
• Taking your HIV medication and any other treatment properly.
• Avoiding infection with hepatitis B or hepatitis C.
• Not smoking.
• Eating a good, balanced diet.
• Exercising regularly.

There is an online tool that can calculate the risk of HIV disease progression for people about to start HIV treatment, and for people who have been taking HIV treatment for six months. It is available here: http://www.art-cohort-collaboration.org.