The losses enabled him to avoid paying income taxes for eight of those years. But the red ink did not cost him his standard of living, because most of the money was borrowed, and because he was buffered by his father’s wealth.

A lawyer for Mr. Trump challenged the findings.

Takeaway: Year after year, Mr. Trump appears to have lost more money than nearly any other individual American taxpayer during the decade. Read other takeaways here.

How we did it: While The Times did not obtain the president’s actual tax returns, it received the information in the returns from someone who had legal access to it. The Times was then able to find matching results in the I.R.S. information on top earners, a publicly available database.