Premium Bond provider National Savings and Investments (NS&I) accidentally paid out around £600 to more than 3,000 savers last year.
The mistake cost the Government-backed bank around £2million, according to its annual accounts.
Some savers could have received more, or some could have received less, as the £600 figure is just the average amount.
The mistake happened after the NS&I paid a higher interest rate to people who had Guaranteed Growth Bonds and Guaranteed Income Bonds before they needed to.
NS&I told The Mirror it implemented the interest rate change on October 26, 2022 - when it should have been brought in on December 1.
The mistake was spotted and corrected on November 3, 2022.
However, it did mean those with Bonds maturing between October 26 and November 3 had access to a higher interest rate than they were entitled to at the time.
These customers were paid more money than they should've been paid.
However, there is even more good news for the 3,265 savers caught up in the blunder.
NS&I has confirmed it will honour the higher rates paid and all those affected will not have to pay any money back.
An NS&I spokesperson told The Mirror: “On 26 October 2022, an interest rate change, due to be made to Guaranteed Growth Bonds and Guaranteed Income Bonds on 1 December 2022, was implemented early in error.
"This was corrected on 3 November 2022, but the error resulted in those customers with Bonds maturing between 26 October and 3 November having access to a higher interest rate than they were entitled to at the time.
"We honoured the higher interest rate they were offered in error.”
NS&I Premium Bond winners for July have been released today and two Brits are £1million richer.
The first big winner is based in Staffordshire, and bought their winning bond 493HK711899 in March 2022.
This now millionaire held £48,750 in Premium Bonds.
The second £1million winner is from Norfolk with the bond number 246DR645231 - this was bought back in May 2015 and they have £20,000 IN Premium Bonds.
