I can make future SEP IRA contributions from dividends on taxable investments that will be tax-free as a result of both 2011 tax extension and SEP IRA deductions.

Is the correct and am I on the right track?

I'm not sure I understand your plan, but a couple of notes on your assumptions. First, I wouldn't count on a continuation of today's tax rate for long-term cap gains and qualified dividends being extended past its 12/31/2012 sunset. But I don't see this as being all that important because of my second note.

Once money is in your pocket its source is irrelevant. So, there's really no tracking of your tax-deferred (not tax-free) SEP contributions. One could just as easily say you used your taxable business profits for that and your tax-free dividends to feed your Twinkie habit.

Phil
Rule Your Retirement Home Fool