I'm defintely not a tax expert but have been trying to find more information on the two different opinions expressed on this topic. I'm leaning towards the fee is deductible on Schedule C from two other sources on the web:
https://www.investopedia.com/ask/answers/102814/what-credit-card-fees-are-tax-deductible.asp with "Businesses can also deduct any credit or debit card processing expenses involved with paying their taxes." and Schedule C is called out earlier in the article.
And on the IRS payment page itself: https://www.irs.gov/payments/pay-your-taxes-by-debit-or-credit-card under "Additional Information" it says "Card processing fees are tax deductible for business taxes."
So to me, what KatrinaB48 says seems to make sense...like the only reason I'm paying estimated taxes is due to self employment/business income, so card processing fees associated with that are business expenses.
There is a bit of interpretation here and it would be great if there was an official IRS statement somewhere specifically confirming this stance...
