Former Vice President Joe Biden Joe BidenPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Hillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Fox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio MORE on Tuesday released his tax returns from 2016 to 2018, showing his income increased significantly after leaving office.

Biden's federal tax return for 2016, his last full year as vice president, showed adjusted gross income of nearly $400,000, while his 2017 federal tax return reported adjusted gross income of more than $11 million.

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His 2018 federal tax return reported adjusted gross income of nearly $4.6 million.

Biden filed his tax returns jointly with his wife, Jill, during those three years

The release of the documents comes during the former vice president's 2020 presidential campaign. Many of the other Democratic presidential candidates released their tax returns earlier this year.

Biden's income of $15.6 million in 2017 and 2018 greatly exceeds the incomes reported on the tax returns of other prominent 2020 candidates, including Sens. Bernie Sanders Bernie SandersThe Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power Bernie Sanders: 'This is an election between Donald Trump and democracy' The Hill's 12:30 Report: Trump stokes fears over November election outcome MORE (I-Vt.), Kamala Harris Kamala HarrisHundreds of lawyers from nation's oldest African American sorority join effort to fight voter suppression Biden picks up endorsement from progressive climate group 350 Action 3 reasons why Biden is misreading the politics of court packing MORE (D-Calif.) and Elizabeth Warren Elizabeth WarrenHillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns On The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline Democratic senators ask inspector general to investigate IRS use of location tracking service MORE (D-Mass.), as well as South Bend, Ind. Mayor Pete Buttigieg Pete ButtigiegBillionaire who donated to Trump in 2016 donates to Biden The Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November Buttigieg stands in as Pence for Harris's debate practice MORE.

Harris and her husband reported the next highest amount of income in 2018, just under $1.9 million.

The former vice president's campaign said that the Bidens' income in 2016 primarily came from Joe Biden's salary as vice president and Jill Biden's salary as a professor at Northern Virginia Community College.

The majority of the Bidens' post-presidential income — more than $10 million in 2017 and about $2.3 million in 2018 — came from book payments and paid speaking engagements.

Joe Biden also earned about $370,000 in 2017 and about $405,000 in 2018 from being a professor at the University of Pennsylvania. Jill Biden continued teaching at Northern Virginia Community College in those years.

The Bidens had effective tax rates of 23.5 percent, 33.9 percent and 33.4 percent for 2016, 2017 and 2018, respectively. They donated to charity 1.5 percent of their adjusted gross income in 2016, 9.2 percent in 2017 and 6 percent in 2018.

During the 2008 campaign, the Bidens faced criticism for regularly reporting annual charitable contributions of less than $1,000 in preceding years. In 2018, the Bidens donated a greater percentage of their income to charity than many of the other 2020 presidential candidates did.

The former vice president's campaign said the couple filed amended 2017 and 2018 tax returns following a "comprehensive review" of their tax filings.

The original 2017 tax return unintentionally double-counted a charitable donation and failed to include income and associated withholdings from the last few weeks that Joe Biden served as vice president.

The original 2018 tax return included a deduction for a donation to a British charity associated with Prince Harry that doesn't have a 501(c)(3) designation.

In addition to releasing his tax returns from 2016 to 2018, Joe Biden also released a financial disclosure form that covers the period from Jan. 1, 2018 through May 31, 2019.

Biden's campaign said the form shows that the former vice president earned about $3.2 million through an S-Corporation during that period for writing and speaking engagements. Many of the fees he was paid for speaking engagements were part of his book tour.

Biden released his tax returns on an annual basis while he was vice president, and also released 10 years of tax returns in 2008. That contrasts with President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE, who has not made any of his tax returns public.

Vice President Mike Pence Michael (Mike) Richard PencePence vows for law and order everywhere Trump met with chants of protest as he pays respects to Ruth Bader Ginsburg The Hill's 12:30 Report: Ginsburg lies in repose MORE released tax returns from 2006 to 2015 during the 2016 presidential campaign, but hasn't released tax returns since taking office.

Trump has said that he won't release his tax returns while under audit, though the IRS has said that audits don't prevent people from making public their own tax information.

House Democrats are trying to obtain Trump's tax returns under a provision of the federal tax code that allows the chairs of Congress's tax committees to request tax returns from the Treasury Department. Last week the Ways and Means Committee filed a lawsuit, asking a judge to order Treasury and the IRS to comply with their requests and subpoenas for Trump's tax returns.

- updated at 6:30 p.m.