[year] 年 + [month] 月 + [day] 号 / 日 [large unit] → [small unit]
A Chinese date runs from the largest unit to the smallest: year, then month, then day.
The same principle governs addresses, times and names – country before city, hour before minute, surname before given name.
2026 is 二〇二六, not 两千零二十六. Each digit is said on its own, and 〇 is the zero.
一月 January through 十二月 December. There are no month names to learn.
A form or a notice uses 日: 9月25日.
今天九月二十五号 is the ordinary sentence. Adding 是 is correct but heavier, and the negative requires it: 今天不是二十五号.
几号 asks the day of the month, 几月 the month.