You will forget why you wrote code a certain way. In two months, you will open a program and wonder what you were thinking. Comments remind you. Good comments explain why, not what. The code x = x + 1; already shows you are adding one.
A comment saying // Increment day counter after midnight provides context the code does not. Avoid excessive commenting. If your code needs comments everywhere, it is probably too complex.
Add comments only where the reasoning is not obvious.