Both my employer and Intuits' Mint platform offer $20 discounts on TurboTax, but I've already paid via credit card for the full price. Am I eligible for a $20 refund?

The discount is off the regular prices ... and those are currently discounted so you got the reduction already.

The regular price for TurboTax Premier was $100, no? If so, with a $20 discount it would have been $80. I paid with a credit card rather than deducting from the return as well.

Premier is normally $80 and is discounted to $60  plus the state fee of $40 = $100    The discount is off the reg federal price not the total including the state fee ... both prices are currently discounted but the discount will disappear in March ... this is when your discount offer really matters. <a rel="nofollow" target="_blank" href="https://turbotax.intuit.com/personal-taxes/online/">https://turbotax.intuit.com/personal-taxes/online/</a>