Democratic presidential candidate Joe Biden used a tax loophole that the Obama administration tried and failed to close, substantially lowering his tax bill.

Mr. Biden and his wife, Dr. Jill Biden, routed their book and speech income through S corporations, according to tax returns the couple released this week. They paid income taxes on those profits, but the strategy let the couple avoid the 3.8% self-employment tax they would have paid had they been compensated directly instead of through the S corporations.

The tax savings were as much as $500,000, compared to what the Bidens would have owed if paid directly or if the Obama proposal had become law.

“There’s no reason for these to be in an S corp—none, other than to save on self-employment tax,” said Tony Nitti, an accountant at RubinBrown LLP who reviewed the returns.

“As demonstrated by their effective federal tax rate in 2017 and 2018—which exceeded 33%—the Bidens are committed to ensuring that all Americans pay their fair share,” the Biden campaign said in a statement Wednesday.