Firstly, it is important to understand how credit card processing fees work. 

When a customer pays with a credit card, the payment goes through a payment processor who charges a fee for their services.

The fee usually consists of a percentage of the transaction amount plus a flat fee per transaction. 

These fees can vary depending on the card type, the payment processor, and other factors. 

To deduct credit card processing fees, you need to keep accurate records of your transactions and fees.

This will help you calculate the total amount of credit card processing fees you paid during the year. 

The fees can be deducted as a business expense on your tax return, reducing your taxable income and lowering your overall tax bill.

To calculate credit card processing fees, you can use online calculators or consult your payment processor.