I had to repay entire subsidy in the amount of $15,000.00 when I filed my taxes in February 2018. Did to having withdrawn money from IRA to purchase a home. Can I deduct the entire $15,000 when I filed this year?
I guess this was because the withdrawal put you over 400%FPL. Too bad it wasn't a Roth IRA open at least 5 years :-)
If you received excess APTC in 2017 and had to repay it (when filing in early 2018) it counts as a medical expense on your 2017 return. For most people this means a Schedule A deduction iff you itemize (and exceed the 7.5% floor). As quid hints, health insurance for self-employed is handled differently, but Is "premium tax credit repayment" deductible as health insurance cost for self-employed? got an answer from the IRS that it works similarly for this case.
Note the links in that Q are to the web version of pub 502 which changes every year and is already updated for 2018, although this point hasn't changed. If you need to confirm, prior-year publications are available in PDF at https://www.irs.gov/forms-pubs-prior-search?search=502
You can amend for a refund up to 3 years from the filing deadline (or actual filing if later, or 2 years from payment if later, but it doesn't sound like those apply to you).