In order to translate Biblical date information into B.C. dates, there are a few things we must understand.
The first thing we need to know is that in ancient times different nations followed different calendars. The Babylonian year began in the spring. The Jewish religious year began in the spring, but their civil calendar which recorded the reigns of kings began in the fall. Dates in most nations were recorded by the year of the king's reign.
We sometimes designate the year of a Biblical event by giving two years separated by a slash mark. For example: 594/593 B.C. In this case the event would have occurred sometime in the Babylonian (or Jewish) calendar year which began in the spring (or fall, depending on which nation) of 594 B.C. and ended in the spring or fall of 593 B.C.
Another thing to remember is what is called a king's "accession year." This was the period intervening between a new king's coronation and the end of that calendar year. The "first year" of a king's reign was considered to be the first full calendar year, not the first 12 months, after his coronation. Whatever period remained from the time he became king until that calendar year ended, was considered his accession year.
A final thing to keep in mind is what we call "inclusive reckoning." To illustrate this method of time designation, let's think of the crucifixion of Christ. The Bible tells us that Jesus was crucified on a Friday afternoon and resurrected on a Sunday morning. Although he was dead for less than 48 hours, the Bible refers to it as "three days." That is because both the first and last days of the period were counted. Inclusive reckoning means that if any portion of a day (or year) was involved, that portion is referred to as one day (or year). We would consider July 1, 1998 to July 1, 2000 to be two years. But reckoned inclusively, it would be referred to as three years. Biblical time periods were often, but not always, reckoned inclusively.