The Internal Revenue Service is sending up to $1,400 to about 1 million taxpayers who qualified for Covid-19 stimulus checks in 2021 but didn’t take advantage of them.

In an unusual move, the IRS is proactively issuing payments to taxpayers who failed to claim the Recovery Rebate Credit, a tax credit that allows people to receive the Economic Impact Payments – also called stimulus checks – they received in the year missed 2021. Originally designed as a self-help loan, the agency now ensures that eligible taxpayers receive the payments they are entitled to.

“When we looked at our internal data, we found that one million taxpayers had failed to claim this complex credit even though they were actually eligible,” IRS Commissioner Danny Werfel said in a news release. “To minimize hassle and make this money available to eligible taxpayers, we are making these payments automatically, meaning these individuals do not have to go through the extensive process of filing an amended tax return to receive them.”

If you haven’t filed a 2021 tax return yet, you can still qualify for the credit — but you must do so by April 15, 2025, according to the IRS.

The stimulus check, part of the American Rescue Plan Act of 2021, was the final payment of financial relief during the Covid-19 pandemic.

Claimed on a tax return and called the Recovery Rebate Credit. It provides up to $1,400 per person, with the exact amount dependent on adjusted gross income and phased out at higher income levels:

• Individual applicant: You’re eligible for the full $1,400 if your AGI was $75,000 or less in 2021. The credit begins to decline at income above $75,000 and stops completely at $80,000.
• Marriage together: You’re eligible for the full $2,800 (for two people) if your combined AGI was $150,000 or less in 2021. The credit begins to decline when total income exceeds $150,000 and ends completely at $160,000.
• Relatives: Families can receive $1,400 for each dependent in 2021 regardless of age, but the amount is subject to the same income phase-out limits as the first-time applicant.

The IRS will automatically send payments to taxpayers who meet the requirements, including those who filed tax returns with blank or $0 entries in the Recovery Rebate Credit data field but were still eligible for the credit.

No action is required for eligible taxpayers to receive these payments, unless you have not yet filed a 2021 tax return.

Payments are being sent now and should arrive by the end of January 2025 “in most cases,” according to the IRS. Payments will be automatically deposited or sent by check using the bank information listed on the taxpayer’s 2023 tax return. Eligible taxpayers should also receive a separate letter informing them of the payment.

Would you like to earn extra money alongside your job? Enroll in CNBC’s online course How to earn passive income online to learn more about common passive income sources, tips for getting started, and real-life success stories.

Plus, Sign up for the CNBC Make It newsletter Get tips and tricks for success in your career, with money and in life.