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Are 'no interest if paid in in x months' credit cards worth it?
I too am a full-monthly-statement-balance payer and I received a balance transfer offer from my credit-card company. This one was quite different from many others that I have read about on this forum. I could do a balance transfer for any amount up to $X from another credit card, or use the enclosed "checks" to pay  some other (non-credit-card) bills, and I would not have to pay any interest for 12 months on the amount thus borrowed.  But, There would be a 2% service charge on the amount I was borrowing. This amount would be billed on the next monthly statement, and it would have to be paid in full by the due date of that month's payment, that is, within the 25-day grace period allowed for payment of monthly statements. Else, interest would start being charged on the unpaid part of the service charge at the usual humongous rate of H% per month. If I had not paid the previous month's balance in full, I would be charged interest at H% per month on the service charge starting from Day One; no free ride till the due date of the next month's statement. Of course, the balance carried over from last month would also be charged interest at H%. If I had paid last month's bill in full, but there were any other charges (purchases) during the current month, then  unless the entire amount due, this month's purchases plus service charge and that "interest-free-for-twelve-months loan"  balance was paid off within the 25-day grace period, my purchases would be deemed unpaid and would start being charged interest. In short, the only way to avoid paying interest on the amount borrowed was to start with a card showing a $0 balance due on the previous month's statement, not make any charges on that card for a whole year, and pay off that 2% service charge within the grace period. It might also have required that one-twelfth of that interest-free loan be repaid each month, but  I had stopped reading the offer at this point and filed it in the round circular file. In short, while @JoeTaxpayer's tale of how "As a pay-in-full user, I've used the zero rate to throw $20K at the 5.25% mortgage" is undoubtedly how things worked once, it is not at all clear that they still work that way. At least, they don't work that way for me.  Heck, once upon a time, for a period of about 3 months, you could earn 1.5% interest per month from the credit card company by overpaying your credit card bill considerably. Their computers then just "added on" 1.5% interest by multiplying your credit balance -$X by 1.015 and so you got 1.5% per month interest from the credit card company. The credit card agreements (and the software!) got changed in a hurry, and nowdays all credit-card agreements state in the fine print that if you overpay your bill, you don't earn any interest on the overpayment.