Among the mysteries of the sinking of the Titanic, such as why the captain was speeding through a known glacier field and what happened to the bodies that went to the ocean floor, is how much its wealthiest passengers were actually worth.

The net worth contained in the doomed steamer’s first-class cabins—estimated to total as much as half a billion dollars—is a large part of the allure of the Titanic’s brief history. But financial reporting was practically nonexistent when the ship sank in April of 1912, and the first income tax was not enacted until the following year.

So while it’s generally accepted that John Jacob Astor IV was the richest man in the world when he went down with the ship, estimates of his personal fortune remain just that—estimates. “We have no data at all,” David Nasaw, a historian of the Gilded Age and author of a 2007 biography of Andrew Carnegie wrote in an email. “With no income taxes, there's no real evidence to go by as to how much he was worth.”

The most common figure given for Astor’s real-estate holdings is based on his bequest to his survivors. A prenuptial agreement gave his second wife and widow, Madeleine, who escaped on a lifeboat while still pregnant with the couple’s baby, a trust fund worth $5 million. His daughter Ava and the unborn child got a total of $8 million in trust, with the bulk of the fortune, $72 million, going to his son Vincent. These bequests amount to about $90 million—or $2.1 billion in 2011 dollars.