Trimming a New Year debt hangover may be fruitless if you ignore fundamental rules of engagement with a credit card balance transfer offer, said financial research company CANSTAR.

If ever there's a time when a credit card balance hits home, it's the Christmas/New Year period.

"It is not uncommon for people to lose sight of their credit card balance during the festive season," CANSTAR Financial Analyst, Adam Beu said.

"Advertised credit card balance transfer offers can look very attractive at these times, particularly if you have a rather large credit limit and the interest charges are too high."

According to CANSTAR, it's not just credit card balances that can be transferred. Many banks are also willing to let customers transfer hire purchase (credit contract) balances from the likes of Q Card, GE Creditline, Farmers Card and more.

"Choosing the right balance transfer for your individual situation is a step in the right direction towards pruning personal debt.

"However, there are a few things that could bring you undone if you're not wary," Mr Beu said.

The four main things to avoid in balance transfer deals are:

1. Pay off your Balance Transfer before you purchase

Most Credit Card issuers apply your repayments to the outstanding balance that has been transferred first, rather than any new purchases, which would attract a higher interest rate. Clever customers can get around this by refraining from spending money on the new card while slowly paying off the balance and taking advantage of the low rate. Only after the balance is paid off in full should you spend on the card.

2. High revert rates

After the advertised number of months - these vary from 6 months to the life of the balance - all unpaid balances are transferred to the standard interest rate. It's important to know what this 'revert' rate is, as it can be as low as 12.9% or as high as 19.95%. As a general rule, before switching credit cards, consumers should know the promotional rate, when it expires and the rate they will pay after expiration.

3. No interest-free days

There are no loyalty points or interest-free days on the balance transferred. Interest is charged from day one on balance transfers.

4. Different introductory rates

When transferring from more than one card - such as a Q Card and a Visa card to one new credit card, there may be different introductory rates. The fine print in some cards say that where you've made more than one balance transfer, payments may be allocated to the balance transfer with the lowest interest rate first.

One final tip, look out for useful balance transfer calculators on banking websites.

CANSTAR researched 69 credit cards offered by 13 lenders in its latest credit cards star ratings report.

The report makes a useful shortlist of cards, according to four spending types - habitual, occasional, everyday and big spender.

"Matching your spending and repayment behaviour with the right card is the first step towards a successful relationship," Mr Beu said.

The complete credit card star ratings report and results are available for consumers on www.canstar.co.nz.