Prison suicides are costing the taxpayer up to £300 million a year, according to estimates by a penal reform charity.
Growing inmate numbers, overcrowding and staff cuts have fuelled a 46% rise in suicide rates over the last three years, according to the Howard League for Penal Reform.
It said public sector funding is being spent on dealing with the aftermath of the deaths when it could be used to prevent them.
Frances Crook, chief executive of the Howard League for Penal Reform, said: "No one should be so desperate whilst they are in the care of the state that they take their own life.
"Similarly, when conditions in prisons are so dire that people are taking their own lives at a rate of one every four days, no one should have to rely on economic analysis to make the case for change.
"Nevertheless, today's briefing paper shows how greater investment in suicide prevention would make financial sense, generating savings for public services that would benefit everyone."
The charity took the cost of a suicide in the community and estimated the additional costs that are generated by a death in the penal system, including investigations by the prisons ombudsman and the coroner, legal representation for prison staff and contributions to funeral costs.
It estimates that the cost to taxpayers is between £160m and £300m a year.
Andy Bell, deputy chief executive of the Centre for Mental Health, said: "Every loss of life due to suicide is a personal and family tragedy.
"Today's report also demonstrates the wider costs of suicide deaths in prison. It is a reminder of how important it is to take action to protect the mental health of all prisoners and to ensure people with mental health difficulties are offered help as quickly as possible when they come into contact with the criminal justice system."
It comes after Prime Minister David Cameron announced plans to overhaul the way prisons are run, with governors given greater freedom over the day to day running and the introduction of performance league tables.
Shadow prisons minister Jo Stevens said: "This shocking report makes for disturbing reading and is yet more evidence of the growing prison crisis taking place on David Cameron's watch.
"Quite simply, the policies of the Tory Government have led to greater overcrowding, more assaults against staff and a rise in violence and self-harm.
"If ministers want to be taken seriously as prison reformers they must urgently tackle the appalling conditions in our prisons and make mental health a real priority."
Prisons minister Andrew Selous said: "We take our duty of care to prisoners extremely seriously and on any given day provide support to over 2,000 prisoners at risk of self-harming.
"However, as the Prime Minister has made clear, our prisons need reform. That includes allowing governors to work with NHS England to tailor their mental health services, so that prisoners in their care get the support they need."