Mako and her college classmate Kei Komuro, a commoner, announced their engagement last September and were to wed in November.
In the context, the Imperial Household Agency cited "a series of important ceremonies next year," apparently meaning the planned handover of the Chrysanthemum Throne. No new dates for the wedding or its preceding rituals were given.
Mako is Emperor Akihito`s oldest grandchild. The 84-year-old emperor is to abdicate on April 30, 2019, with Crown Prince Naruhito taking the throne the next day.
The surprise delays less than a month before a planned ceremony in March to formalize the couple`s engagement left many people puzzled.
Agency official Takaharu Kachi told reporters the decision was not related to tabloid reports about disputes between Komuro`s mother and her former partner over money she borrowed to cover her son`s tuition and never repaid.
Mako said in a statement released by the agency the delay was due to insufficient preparations.
Mako wrote we have come to realize the lack of time to make sufficient preparations for various events leading up to our marriage this autumn and our life afterward and we believe that we have rushed various things too much.
Mako said the couple wishes to think about marriage more deeply and concretely and give more time to prepare for their marriage and life together afterward. She said Akihito and Empress Michiko expressed respect for the couple`s decision.
The palace requested 150 million yen ($1.4 million) as part of its fiscal 2018 budget to cover the costs of the wedding and the process of starting her life outside the royal family. Under the imperial household law, female members lose their royal status when they marry a commoner.
Those who are concerned about the future of the royal family with shrinking membership want to allow women to succeed the throne and others to keep their royal status so they can keep performing public duties, but a government panel has avoided the divisive issue.