Moving to a seven-day service will cost between £1bn and £1.4bn, the findings suggest.
But patients could benefit twice as much if the funding was diverted to other priorities, according to the research by health economists from the University of Manchester and the University of York.
The findings directly challenge government plans to develop a seven-day health service by 2020.
Seven-day GP services
Health secretary Jeremy Hunt pledged to transform general practice – and other parts of the NHS – into a seven-day service within days of the Conservative general election victory.
A GPonline poll also found that nine out of 10 readers believe the government’s goal of seven-day general practice by 2020 is not achievable.
The researchers said that the cost of moving to a seven-day NHS would exceed the NICE cost-effectiveness threshold for health interventions by a factor of between 1.5 and 2.4, in findings published in the journal Health Economics.
NHS death rate
The researchers estimate that higher death rates over the weekend mean that up to 5,353 ‘excess deaths’ occur each year on Saturdays and Sundays.
Based on NICE’s threshold, if the NHS could eradicate these deaths for £730m it would be a cost-effective intervention.
But seven-day services are likely to cost up to twice this amount, and there is no guarantee that all excess deaths will be prevented, or that weekday care will not deteriorate as staff are diverted to weekend duties, the researchers warn.