The investigation found that many royals have been paying below market rents, while some have their accommodation costs paid for by the King and others sub-let the properties for an unknown amount.
The report has sparked accusations that the Royal Family has shown "total contempt for the taxpayer", especially in cases where support was provided to non-working royals.
So what are the Royal Family's residential property arrangements?
Andrew Mountbatten-Windsor
The former prince has received an undisclosed private income from subletting three cottages on his Royal Lodge estate for two decades, while paying a peppercorn rent.
"Three cottages on the Royal Lodge estate were also sublet with income generated from subletting payable to Andrew Mountbatten-Windsor," the report said.
Andrew was entitled to sublet up to three properties on the Royal Lodge estate in Windsor Great Park under the terms of his lease.
No figures have been provided of how much income the properties generated, with the NAO saying the figure was private.
However, royal insiders suggested that Andrew's subletting did not produce a profit because the rate only covered maintenance and running costs.
Andrew left Royal Lodge earlier this year and moved to the King's private Sandringham estate in Norfolk in April, after he was charged with misconduct in public office over his links to Jeffrey Epstein.
The late Queen's second son, who was stripped of his prince title and dukedom by Charles over his friendship with the billionaire sex offender, was not asked to provide figures for the amount of money the sublets produced.
It has been widely reported that Andrew may not receive the compensation he is due for giving up his lease, which would be a pay out of between £301,967 and £488,342, depending on the condition of the property and the date the lease is officially surrendered.
It is also not known whether Andrew's sublet properties were consistently rented out, but his subletting of the residences ended in April 2026.
Princess Beatrice and Princess Eugenie
The King has footed the bill for the daughters of Mountbatten-Windsor and Sarah Ferguson, who are non-working royals, to live in accommodation in royal palaces, the report said.
The rents set for their accommodation are also based on out-of-date valuations, the NAO found, in part because royal household properties require tenants with security clearance.
Princess Eugenie's rent for Ivy Cottage in Kensington Palace is based on the 2018 valuation between 2020 and 2021 and Princess Beatrice's apartment in St James's Place on a 2020 valuation.
The princesses were then only required to pay a percentage of that value, with both paying a percentage between 50% to 68% of the market rent since 2020.
However, both their rents are actually paid to the royal household by Charles out of the Privy Purse, made up of his Duchy of Lancaster income and other private funds.
Eugenie is said to have carried out refurbishments at Ivy Cottage at her own expense.
It's believed the arrangement was put in place by the late Queen Elizabeth II for her granddaughters, and Charles has continued it.
The Sovereign Grant, which pays for the Royal Family's official duties and the upkeep of royal palaces, is met from public funds in exchange for the King's surrender of the revenue from the Crown Estate.
The Prince and Princess of Wales
William and Kate pay £307,200 a year for their home, Forest Lodge in Berkshire, and have avoided peppercorn rent accusations.
The report said the couple signed a "short-term 20-year lease" with quarterly rent payments of £76,800 every three months, and no upfront deposit because they pay for all internal refurbishment costs.
But the Crown Estate paid £396,993 for repairs at the mansion, two of three cottages on the site, the barn and the grounds before the couple moved in.
The tenancy covers the Grade II listed Georgian house, gardens, paddock with 7.4 hectares, a barn, and three cottages.
Prince and Princess Michael of Kent
The late Queen's cousin and his wife, Marie-Christine, have also had their rent paid by the King from the Privy Purse.
The couple sparked a scandal and were dubbed the "Rent-a-Kents" when it emerged in 2002 they paid a peppercorn rent of just £69 a week to live in the grand Apartment 10, despite not being working royals.
When the arrangement emerged, the Kents argued that Queen Elizabeth II had given them the use of the Palace as a wedding present, after MPs on the Commons' Public Accounts Committee demanded they pay full rent.
A commercial rate rent of £120,000 a year was paid on their behalf by the late Queen, but they would need to pay their own way from 2009.
But the report shows the Kents never paid their own rent, after the Queen privately agreed to continue the private funding.
As a result of this agreement, the King has continued to pay their rent, which is now set at 63% of open market value.
The Duke and Duchess of Edinburgh
Edward and Sophie were also found to pay a peppercorn rent after signing a long lease of 150 years in 2007 for Bagshot Park in Surrey with a payment of £5m.
The King's brother and his wife have, like Andrew, generated a private income by renting out the property, letting out the stable to a third party in 2020.
Edward's company Eclipse Nominees Limited is listed as the leaseholder.
They previously held a lease from 1998 to 2007, and committed to spend £1.38m on restoration.
Princess Alexandra and Marina Ogilvy
The late Queen's cousin Princess Alexandra pays an annual ground rent of £1,500 to live at Thatched House Lodge in Richmond Park, which is leased to THL Trust.
The amount she pays changes depending on the time that has lapsed, after a premium payment of £670,000 in 1995, following a previous lease in 1971.
Her daughter Marina Ogilvy has a shorthold lease on a cottage on the Windsor Estate and pays an annual rent of £17,436.
'Taking the public for a complete ride'
Former Liberal Democrat minister Norman Baker, who has long been a critic of royal finances, branded the arrangements as "outrageous".
"The whole thing is outrageous. If you look at Andrew, this is adding insult to injury," he said.
"It shows an absolute total contempt for the taxpayer, not only that Andrew was able to have a peppercorn rent for a gigantic property, but then to make potentially millions on the side from subletting properties.
"The money should have gone to the Crown Estate, not into his pockets."
On Beatrice and Eugenie, he said: "There's no way that non-working members of the Royal Family should be subsidised by the Duchy of Lancaster.
"The Royal Family is yet again taking the public for a complete ride."
He added that any profits made from sub-letting the properties should go to the Crown Estate.
"We are, in fact as taxpayers, subsidising money to go into Andrew's pocket and indeed Edward's pocket," he told Sky News.
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The report will form the basis of the Public Accounts Committee's inquiry into royal properties.
Former Labour MP Baroness Margaret Hodge, who once chaired the Public Accounts Committee, agreed it was "outrageous" that some figures concerning the income royals earned from sub-letting the properties were missing from the report.
"There's a lot of taxpayer money that goes into supporting the Royal Family, quite rightly, but that means we need transparency and we need accountability, particularly at a time when everybody is struggling very much," she said.
"I welcome the report, but there's a lot missing."
Royal commentator, Jennie Bond, said there needed to be "more transparency" around the royal's financial arrangements, especially when it involves private sub-let agreements
"The point of all this is these are part of the Crown Estate," she said.
"The Crown Estate is an independent commercial operation which must be run for profit, and that profit goes directly back to the Treasury.
"In other words, it's public money. And that is why there is public interest in exactly who pays what."
Ms Bond also criticised Beatrice and Eugenie and said she did not understand why they had to "sponge off their uncle" as "grown women".
"They have their own careers. They're both married to a successful businessman," she said.
A spokesperson for the Crown Estate, said: "The Crown Estate welcomes the National Audit Office's review which confirms its leases with members of the Royal Family were agreed in line with independent, professional advice and open market valuations.
"We look forward to discussing the report further with the Public Accounts Committee in due course."
Buckingham Palace declined to comment.
