Meghan Markle appears on the list for the first time after her marriage to Prince Harry in May. The Duchess of Cambridge had a reduced schedule due to the birth of Prince Louis in April. She was on maternity leave until she resumed her actual obligations in September.
The Court's Circular shows how many days each Royal performed official functions.
However, it does not show how many appointments they attended each day they told, or how long they lasted.
According to an analysis of The Sunday Telegraph, Princess Anne attended almost every day of any Royal in 2018, over 180 years.
She is therefore, by her analysis, the most hardworking member of the Royal Family.
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The Queen's only daughter is involved with more than 300 charities, military organizations and regiments and often holds official visits.
She works closely with the Carers Trust, which provides support for those caring for disabled or ill family members she helped launch in 1991.
The princess was followed by Prince Edward, the Earl of Wessex, who worked for at least 170 days.
Last year, he took over much of the work overseeing his father's Duke of Edinburgh Award scheme, and is also associated with several British sports institutions.
He is also chancellor of the University of Bath, which he visits regularly.
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The third on the list was Prince Charles, who participated in more than 160 days of royal functions.
Referring to the work ethic of his father, who recently turned 70, Prince Harry recently commented: "Man never stops."
In all, the Prince of Wales, Royal Princess, Earl of Wessex and Duke of York, conducted royal commitments in 675 days, substantially more than the younger generation.
The queen, now 92, has performed more than 120 days of actual obligations.
These included the reception of foreign leaders in the UK, such as President Trump, who visited in July.
In May, the Duchess of Sussex was added to the Circular Court for the first time.
She joined Prince Harry on a tour of Australia, New Zealand, Fiji and Tonga in October.
The Duchess of Cambridge understandably executed royal commitments in a reduced number of days, just over 50 years, after several months of maternity leave after the birth of Prince Louis.
Her husband, Prince William, had commitments in more than 120 days.