Usually, unexpected tax refunds are due to math errors.
However, there are other possibilities too.
Why did I get an unexpected refund?
The simplest reason that you may have gotten a return you didn’t expect is because of a math error when you filed your taxes. These errors are usually picked up by the IRS and fixed. Read more about it here.
The IRS usually fixes the problem before the checks are sent out, but there are still some that slip through the cracks. If the IRS notices, a tax refund will be sent out with any differences that you overpaid.
Unexpected refunds may also come if you forgot to include that you already paid. This is common among independent contractors and people who are self employed.
If you made an error when filing, the IRS recommends using their interactive tax assistant tool. This will help you figure out if you need to file a new return to fix the mistake.
The IRS will likely fix it if it is a mathematical error or they will send you a letter if they additional information if need be.