Whether it makes sense to amend your return depends on which of these situations you're in:
If You Owe The IRS
If you discover an omission on your tax return that results in you owing additional tax, you need to correct it with an amendment and provide the tax due. Don't delay if this is your situation. If the IRS discovers the omission before you do, they may add interest and penalties to your bill.
If you are Due a Refund
If you find a mistake that should result in getting a larger refund check, you can claim it by filing an amended return. But there are several reasons it may not be worth it.
It May Open a Can of Worms
In many cases, amending your federal return means also amending your state returns. Multiply the hassle if the error spans across two or more years.
It puts a Spotlight on You
While your original return may have passed through the IRS's automated system without a hitch, now that it's amended you can virtually guarantee it will get a closer look. If you have anything else in your return that can trigger an audit, like business deductions, charitable donations, or other credits, this can be a concern.
It May Take a Long Time to Get a Refund
The IRS tries to process your original return within three weeks. No such luck for an amended return. It can take several months to get an amended return processed and see that extra refund, even as long as 1 1/2 years in rare cases.
It Stretches Out the Audit Window
The IRS generally has a three-year window to audit returns and request changes. When you file an amendment, you extend the audit time frame.
It may be Too Late
Depending on when you notice an error and how far it goes back, it may be too late. The deadline to file an amendment is generally the later of three years after the original return was filed, or two years after the tax for that year was paid.
Ultimately you have to weigh the extra money you could get from amending against the potential problems it could cause. If it's worth it, get an amendment filed. Call to get help with an amendment or if you have other tax questions.