Defer income to 2018?

[Todd Willhoite]

Can I defer income to 2018 where the tax brackets are more favorable than 2017 by doing the following strategy? I don't want to tie any more money up in tax deferred accounts, but if I make a deposit to my sep-ira or simple-ira for 2017 and then in 2018 roll it into my roth ira I will get to deduct the contribution on 2017 taxes and pay income taxes on the same amount in 2018, right? But then can I withdraw the deposit from my Roth IRA without penalties? (I am under 59 1/2 years of age. My existing Roth is only 1 year old.)