There can be several reasons to amend a previously filed tax return. This can be done for both Individuals and Business returns. Generally, for a credit or refund, you must file Form 1040-X within 3 years after the date you timely filed your original return or within 2 years after the date you paid the tax, whichever is later. Allow the IRS up to 16 weeks to process the amended return.
Among the reasons to amend are corrections to income, deductions, change of filing status ie from single to married filing jointly etc.
The form used for amending is the 1040X for Individuals and 1120X for C and S corp returns. The process is similar. Though some taxpayers will be willing and able to prepare and file the amended return form, the process can get tricky.
A recent amended forms 1040X for 2015 and 2016 timely filed in Jan, 2021 just were approved. That took 20 months. Of course any return amendment can take shorter or longer than another but this was long process with many communications that was finally resolved by one of the special units after seeking assistance form the Taxpayer Advocate's Office. My client was frustrated many times during this long haul but all that abated when the over $40,000 refund was confirmed by a letter CP49.
For those needing to amend a return you can get all the info at
https://www.irs.gov/forms-pubs/about-form-1040x
for individual returns and there will be a link available for the 1102X for business as well.
For anyone wanting professional preparation my fees are on the site as a starting point. Call anytime.
Best to you,
Donn Marier
DM-Your Own CFO