Under the numbers in your original post you will qualify for up to $4000.00 credit. This is a non refundable credit so you have to do this correctly or you will lose out on your maximum take. The tax on $6000.00 ($30,000-$24,000[standard deduction married/joint]) is $600.00. If you put $1200.00 in to a Roth IRA you net tax is zero after the Savers Credit.( 50% of $1200.00 tax credit to zero you out). If you put the same $1200.00 in a traditional IRA you would reduce your AGI to $4800.00 and reduce your tax savings to $480.00. Less tax savings and lose of tax free withdraw from the Roth. With the Roth you get a 50% bonus. The trad IRA not so much.