You will need to file an amended return with the IRS if you discover an error, change your filing status, add dependents, or if your income, deductions, or credits are incorrect. You will not need to file an amended return to correct math errors or if you left off certain schedules or forms. Generally, the IRS will automatically make corrections or send a request to you to submit left off schedules and forms.
If the IRS owes you money from a prior tax year, you can’t delay in sending in your amended tax return. Generally, to claim a refund, you will need to file form 1040X within 3 years from the due date of your original return or within 2 years from the date you paid the tax, whichever is later. If you don’t, chances are you can kiss that refund goodbye! As a side note, in 2008, the IRS had $1 Billion in unclaimed tax refunds.
Filing an amended return is the right thing to do if your return requires changes. Sometimes finding an extra document or taking another look at a past tax return can reveal some extra money for you.