Charles has taken the step of publishing his payments to HM Revenue and Customs in a bid to aid clarity and accessibility around royal finances.
William, the Prince of Wales initially resisted releasing his own tax payments when he became heir to the throne but has released his financial data as a string of royal reports were published.
Since Charles became King following the death of Queen Elizabeth II in September 2022 he has paid more than Stg 30 million ($A57 million) in tax, while William has made payments of more than Stg 20 million ($A38 million) in tax since becoming the Prince of Wales.
James Chalmers, Keeper of The Privy Purse, said: "When (he was) Prince of Wales, His Majesty disclosed his tax, and he has asked that we make public his combined income and capital gains tax payments as king.
"Today I can share with you that His Majesty's tax payable for 2024-25 was Stg 12.9 million.
"If annual media league tables are to be believed on such matters, that places His Majesty among the top 100 taxpayers in the country for that year.
It has also been revealed that Charles will not live at Buckingham Palace after the completion of a 10-year Stg 369 million refurbishment program as the monarchy seeks to increase public access to the historic building that has been the centre of royal life for almost 200 years.
Royal officials stressed that the king and Queen Camilla would continue to work out of the palace, which will remain "the ceremonial and operational centre" of the monarchy. But for the rest of Charles' reign, the king and queen will remain in nearby Clarence House.
"It is and will remain Monarchy HQ, the crown jewel of our national buildings," Chalmers said.
The announcements come as the royal family tries to shift the narrative after months of embarrassing headlines about the links between the convicted sex offender Jeffrey Epstein and the former Prince Andrew, now known as Andrew Mountbatten-Windsor.
Built in the 1820s, Buckingham Palace has been the London home of every British monarch since Queen Victoria, but had begun to show its age.
In 2017, the royal household began a 10-year program to update obsolete plumbing, wiring and heating. The project is scheduled to be completed next year.
The king and queen have decided to live at Clarence House, a stately home close to the palace where Charles has lived since he was Prince of Wales.
That decision will allow the palace to increase access public access, hosting more events and expanding the number of visitors and tours of the building, Chalmers said. The palace already receives about 700,000 visitors a year.
The release of the financial records showed the Prince of Wales topped the annual list of the most expensive royal trips.
William's three-day visit to Saudi Arabia in February on behalf of the UK government cost a total of Stg 130,000 ($A248,294).
This was just ahead of the travel costs for the King and Queen's four-day state visit to Italy in April 2025.
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