The agency will start accepting returns on Feb. 12, about two weeks later than usual. But you still have to file by April 15.

The start of tax filing season is postponed by a couple of weeks this year, but the government says it expects to pay most refunds reasonably quickly.

Typically, the Internal Revenue Service begins accepting and processing individual income tax returns in late January. But the agency has pushed back the start of filing to Feb. 12 for returns for the tax year 2020.

The shift was needed, the I.R.S. said, to allow the agency to update and test its systems to reflect late-year tax changes approved by Congress, including a second round of economic stimulus payments.

“This start date will ensure that people get their needed tax refunds quickly while also making sure they receive any remaining stimulus payments they are eligible for as quickly as possible,” the I.R.S. commissioner, Charles P. Rettig, said in prepared remarks.

This is shaping up to be another challenging tax season for the I.R.S., which has struggled in recent years with reduced budgets that have forced it to make do with fewer workers and outdated computer systems. During the pandemic, it has also had the extra work of distributing stimulus checks.

Because of the coronavirus, the I.R.S. was delayed in processing some returns, particularly those filed on paper, according to the Taxpayer Advocate Service, the arm of the I.R.S. that speaks for filers. Though most people file returns electronically, about 16 million paper returns were filed last year. As of Dec. 25, there were still nearly seven million unprocessed individual returns from tax year 2019, according to the I.R.S. website.

Even so, the I.R.S. said, most taxpayers due a refund for the 2020 tax year will get it within three weeks if they file electronically and have the money deposited directly into their bank account. The average refund in recent years has been more than $2,500. Many families use refunds to pay bills or use it as a kind of forced savings plan.

The change in the start of filing season raised concerns about recipients of antipoverty tax credits, like the earned-income tax credit and the child tax credit, who typically have lower incomes and file early to get refunds quickly. But people claiming the credit can expect to receive their refunds beginning in early March, which is typical, as long as there are no issues with their tax returns, the I.R.S. said.

“This would be the same experience for taxpayers if the filing season opened in late January,” the agency said. By law, the agency cannot issue refunds to people claiming the credit until after mid-February, as part of anti-fraud efforts.