Why do August and July have 31 days?

August and July each have 31 days due to historical decisions made during the Roman calendar reforms. Originally, the Roman calendar had a different structure, but when Julius Caesar implemented the Julian calendar in 46 BCE, he assigned 31 days to July in honor of himself. Later, Emperor Augustus took the month of Sextilis and renamed it August, giving it 31 days to match July, ensuring both months had equal length. This decision helped standardize the calendar we use today.