Why didn’t a 275.00 donation to charity lessen my federal amount owed?

First, was the $600 in cash? Only cash donations ("money") count for this special deduction.

Second, have you already entered the cash donation in the Charitable Donations section?

Third, have you made at least one pass through the Review? At one point, the $600 was handled in the Review.

Fourth, are you taking the Standard Deduction? This special deduction is only for those who don't itemize.

Finally, have you looked at your 1040 to make sure that the $600 is not already in line 12b on the 1040?

If you are using he desktop software, go into Forms mode (upper right) and look at the 1040.

If you are using an Online product, on the left, click on Tax Tools, then click on Tools underneath it, then in the center, click on View Tax Summary, then back on the left, click on Preview my 1040.