Nuffield Health has already raised its target of £15m from a new bond but will continue to accept investments until the advertised closing date of 18 June, the charity announced today.
The five-year bond, launched by the healthcare charity on 15 May, will pay 6 per cent a year, and is open to investments of between £1,000 and £250,000. The charity says it is the largest bond ever offered by an operational charity.
Larger bonds have previously been issued by the Wellcome Trust, which gives grants for medical and scientific research.
KP Doyle, group chief financial officer for Nuffield Health, said: "We are thrilled that we achieved our target for the Nuffield Health Bond and to do so in a relatively short period of time is testament to the strength of our offer.
"Any surplus money the charity makes is always reinvested. The £15m and further funds raised will help us with our mission to make a real difference to the future of healthcare in the UK."
Nuffield recently announced that its turnover increased to £645m in 2012, a 12 per cent increase on the previous year.