What is the difference between 几月几号 and 几号?
There is nearly no difference between 今天几月几号？ and 今天几号？.
Usually for short and orally, we use 今天几号, instead of 今天几月几号. Because we usually know which month currentlly, and it's a present tense or on going tense.
If the date is the last days or the first days of the month, ask 今天几号 will not confuse.
For example.
(比如今天8月3号)
A: 今天几号？
B: 3号啦。
A: 啊！已经到8月份了啊。(时间)过的好快。
Another sample。
（比如今天7月30号）
A: 今天几号？
B: 30号啦。
A: 啊！快到8月了啊。(时间)过的好快。
But if you ask someboby 今天几月几号, then he may say &quot;现在是几月份，你这都不知道吗？？？&quot;. He may means you have no sense of time(date).