The gap between what Americans owe the government and what they actually pay is large and growing, the IRS said Thursday, estimating the “tax gap” for 2021 at more than $600 billion.

IRS Commissioner Danny Werfel said he’s dedicated to reducing that figure as a matter of “fairness” to those who pay on time and in full.

About 85% of Americans do comply with the law, the IRS said, resulting in some $688 billion that wasn’t paid on time in 2021. Late payments, audits and fines will reduce that number to a net tax gap of about $625 billion.

That amount is 16% higher than in 2020 and 30% higher than in the early years of the Trump administration.

The IRS dropped the new numbers into a raging debate in Washington over how aggressive the IRS should be in sweating out more money from Americans.

The Biden administration is pushing for an aggressive approach, saying the wealthy aren’t paying up, while Republicans are resisting, warning that a supercharged IRS will oppress even law-abiding taxpayers.

“This increase in the tax gap underscores the importance of increased IRS compliance efforts on key areas,” Mr. Werfel said in a statement announcing the numbers.

He said the climate budget law Democrats pushed through Congress and signed by President Biden last year will help by pumping tens of billions of dollars into enforcement.

The federal government collected $4 trillion in total revenue in fiscal 2021 and spent $6.8 trillion as the government poured money into pandemic relief efforts.