If there is one thing people hate about credit cards, it’s their often-high interest rates. With that in mind, what could be better than a no-interest credit card? Borrow money with a 0% interest credit card, and only pay back what you spend. The advertisements for such cards can be irresistible.

Before you run to apply for a 0% interest credit card though, you should know a few important things:

1. That 0% interest rate may only apply to balance transfers.

One of the more common reasons people opt for no-interest cards is the ability to transfer high-interest credit card balances to them to save money. Read the fine print first. A 0% balance transfer rate for six months won’t apply to any new purchases you make. If you are looking for a credit card for purchases instead, what you should look for are “interest-free days.”

2. Interest-fee days vary greatly from one card to another.

Interest-free days are a grace period between the time you make a purchase and the time interest begins accumulating on that balance. If you pay the full debt off within your interest-free days, you never accrue interest. Those interest-free periods can differ significantly from one credit card to the next, and can be a major factor when comparing credit cards if you plan to pay off your balance in full regularly. Even credit cards issued by the same bank can have different interest-free periods. For example, while the ANZ Gold Visa Credit Card offers 55 interest-free days, the ANZ Frequent Flyer Credit Card only offers 44 interest-free days.

3. Credit card companies have to make money somewhere.

If they aren’t earning money from you with interest payments, they’re likely doing it in another way. You may have to pay an annual or monthly fee for example. There may be other hefty fees involved for balance transfers, late payments, cash advances, or other transactions. Before choosing between credit cards solely on their interest-free days, compare all of the fees carefully.

Credit cards with interest-free days can be attractive, and when handled properly they can be effective at minimising your overall debt. Remember that good things rarely last forever, and low credit card interest rates are no exception. Your no-interest period will expire, and to reap the benefits you will have to remember to pay off your debts in full before those interest rates kick in. Keep thorough records of your purchases and interest-free periods, and you’ll never be surprised by unexpected interest added to your balance.