Why is the Jewish year different?

Within a month, the days are always numbered from 1 to 29 or 30 in the Jewish

calendar, while in the Civil calendar they are numbered 1 to 30, 31, 28, or 29.

Other differences:

-- The dates on western Civil calendars are written in the 10-digit decimal

system of notation that you're accustomed to seeing everywhere. On the

Jewish calendar, the dates MAY BE written in the system of numeration

that uses characters of the Hebrew alphabet without place values.

-- The months of the western Civil/business calendar, and those of the Jewish

calendar usually begin on different days, and there is a difference in the length

of months and of years. The reason is that the Jewish calendar synchronizes its

months with the visual phases of the moon, just as the Chinese and Muslim

calendars do, whereas the Western calendar departed from that system some

time ago.

Answer:

In addition to what is stated above:

1) The Jewish calendar is unlike the Muslim one in that it adjusts (by leap-month)

to synchronize with the solar year as well as the lunar one.

2) The most obvious difference between the Jewish and Western calendars is that

the Jewish years are numbered from the traditional year of Creation.