Number + 日
日 (rì) means "day" and is the formal way to express the day of the month in Chinese. It appears after a number in date expressions, such as 十五日 (the 15th). It is more formal than 号 (hào), which is used in spoken Chinese.
报告将于六月十五日提交。
Bàogào jiāng yú liù yuè shíwǔ rì tíjiāo.
The report will be submitted on June 15th.
国庆节是十月一日。
Guóqìng jié shì shí yuè yī rì.
National Day is October 1st.
他们定于八月二十日举行婚礼。
Tāmen dìng yú bā yuè èrshí rì jǔxíng hūnlǐ.
They have scheduled the wedding for August 20th.