Is the state deduction really an advantage?

I am a MD resident and can get a state deduction if I use the MD T. Rowe Plan.
My question is if I take the deduction- is it meaningless because you report your state taxes on your federal return. I would have less of a deduction of state taxes paid on my fed return. Obviously, my fed bracket is higher than my state, so when all is said and done does the deduction really help me.
I believe this is called federal offset. How much am I really saving once I take less a deduction on the fed return?
:eek: Just curious because I'm leaning toward an out of state 529 plan and I won't get the deduction.
I hope somebody out there understands my question.
Thanks!

Assuming you itemize your 1040, your state tax deduction is effectively reduced by your federal marginal tax rate.

An example, kept simple. If you are able to deduct $400 from your state tax return based on your MD 529 contributions, and you are in the mythical 25% federal tax bracket, then you would pay $100 more in federal tax. You MD deductions are worth only $300.

Does that answer your question?

TJ