When it can become a problem: - Failing to report the capital gain/loss or the expense properly. - Claiming a deduction for something that is not a real business expense. - Using crypto specifically to conceal income, evade taxes, or launder money. - Ignoring 1099/W-2/payroll reporting rules if you...

Assuming US federal rules, the short answer is: the fee isn't its own deduction line, but it isn't lost either. 1. Paying a business expense in BTC is two things at once. The expense itself (say a $500 invoice) is deductible like any business expense, at its dollar value. And spending the BTC is a ...