Amended returns usually take 3-4 months to process however this year the IRS was shut down for almost 4 months and more than 11 million envelopes piled up and they just started opening them in June ... so expect amended returns this year to take 6 months or more to process and all you can do is check the IRS site once a week until you get a progress report ... https://www.irs.gov/filing/wheres-my-amended-return
