Following Terry's tip on using credit card for investment without mixing the purpose: I have a CC that was used for personal items. Spent say $2000 on it, paid $2000 back to the card to bring the balance back to $0 before I used it for investment purchases and in the hope that I can refinance the investment purchases with my upcoming IP loan and keep those deductible. Weird thing happened this morning that one previous personal transaction of $10 (part of the $2000 personal spending) was not collected and suddenly my account balance is +$10 rather than $0. I have never had a moment before of disliking the extra $10 that much . Would this situation affect the deductibility of my investment purchases?