When I enter my charitable contributions my estimated refund doesn’t change

Charitable contributions only affect your return if you itemize deductions. If you’re using the standard deduction, you won’t see a difference in your estimated refund amount when you enter your charitable contributions.

Credit Karma Tax will automatically select the larger deduction for you though you will have the option to override this selection if you wish. You should still make sure to enter your charitable contributions and any other deductions that you may qualify for.