First, you don’t get a blanket tax exemption. If you sell your main residence and you owned it for at least two years and lived in it for at least two of the past five years, you can exclude $250,000 of capital gains or $500,000 of gains if married filing jointly. If you sell in less than two years for one of the allowable reasons, you can claim a partial exclusion. Let’s say you owned the house for 18 months, that would be 75% of two years so your exclusion would be 75% of $250,000 ($187,500) or 75% of $500,000 ($350,000). If your gain is more than that amount, you will still owe capital gains tax on it.
Second, you do not send any proof with your tax return. You would keep any proofs for at least three years after you filed in case of audit.
Third, you just need to show that you moved early because of the new job. I am sure you have lots of emails and other paperwork documenting your job search and your new job offer, otherwise you would be selling your house and moving blindly. Don’t overthink it.
(If you are selling blindly and hoping to get a new job in your new city but don’t have one lined up, you might still qualify for the partial exclusion. Publication 523 is not specific, and I would need to research this more thoroughly.)
