IRS Link to Form — Found Here

Form 1045 can be used to apply for a refund that might carry-back of up to 5 years, if an individual or trust has overpaid on their taxes, finds Net Operating Losses (NOL), or has section 1256 losses to carry-back.

The 1045 is meant to be the quickest way to get a carry-back refund.

Net Operating Losses from a pass-through entity or business can be carried back up to 5 years now, according to updates to IRC 172(h). Section 1256, which applies to futures contract investing, will allow a carry-back of losses in a 3-year time frame. For such carry-backs, the standard filing is IRS Form 1045.

There is also a Form 1045x, which may be appropriate in situations where the regular 1045 deadline has passed, but the 1045x requires a separate form for each year for which carry-back is being requested. Individuals who miss the 1045 deadline must file an amended Form 1041.

An individual might also need to file a 1040-x to amend the previous tax return if they are self employed, and in some cases they will not need to file the 1040-x, or the 1045 will not be available for the purpose.