The official financial statement was released very recently. It seems that they spent more than the Sovereign Grant due to the exceptional nature of the last year.
" In total, the Royal Household’s net expenditure was reported to be £107.5 million ($136 million), compared to the total Sovereign Grant of £86.3 million ($109.1 million) and the additional income of £9.8 million ($12.4 million).
The Sovereign Grant – an annual lump sum from the government – is essentially an expense account, covering the costs of travel, security, staff and the upkeep of royal palaces. The Royal family’s three main sources of income are the Sovereign Grant, the Duchy of Lancaster and Duchy of Cornwall estates and their personal property and investments.
“Official expenditure was more than the Sovereign Grant and the supplementary income earned, with net expenditure of £107.5 million ($136 million), a 5% increase on the previous year due to significant work relating to the Reservicing of Buckingham Palace and the costs associated with the change of Reign, as well as the impact of the Consumer Price Index rising by 10.1%,” Buckingham Palace said in a statement.
The high official expenditure saw the Sovereign Grant reserve reduce by £20.7 million ($26.2 million) in the last year. (The reserve is a kind of emergency fund for just this kind of overflow expenditure.