Once caveat to dmertz' great answer above. You CAN owe taxes on traditional IRAs that are converted quickly before earnings accrue on new contributions - IF you still own other traditional IRAs that have accrued earnings. The IRS views your entire portfolio (collection) of traditional IRAs -existing and new - as one - and subject to taxation. Taxes would be proportional to the amount you are converting, relative to the value of your entire portfolio of traditional IRAs.
