Spending $25,000 on a credit card over two years is unlikely to earn you even $180 on reward schemes, a survey has revealed.

The study, in the February edition of Consumer, reveals that many credit cards boasting spending rewards actually result in costs to the card holder.

The top card, a BNZ American Express Classic, would net the user $182 of flights if they spent $25,000 over two years and managed their account well enough to pay no interest.

That means a customer would have to spend about $75,000 over two years on this card to get a $500 return flight to Sydney.

The survey warns: "Unless you spend heaps on your card - usually more than $25,000 over two years - and fully pay off your card at the end of each month, most of these schemes won't be worth it.

"At best, you'll be able to enjoy a minor treat after a couple of years of careful points-hoarding. The worst case is you'll be paying more for your minor treats than you would by buying them without using points."

Consumer NZ chief executive Sue Chetwin said average or lower-than-average spenders and people who didn't pay off credit-card debt in full each month were best to avoid rewards schemes and opt for low-interest, low-fee non-reward cards.

High rewards rates were almost always met with a high annual fee - and an extra fee for being part of the rewards scheme.

Because of that, users had to spend at least $12,000 a year and pay the debt off fully every month, just to cover the fee before even earning points.

The cards with higher fees meant users had to spend heavily on them to show a positive return on the rewards programme.

Ms Chetwin said the Westpac Titanium Mastercard, with a fee of $290, would have left Consumer $393 in debt.

Cash-back schemes fared little better, with two National Bank cards topping the list, netting the user $160.

Air New Zealand points can now be earned at more than 3000 Fly Buys outlets. "Fly Buys can also convert to Air New Zealand points, but at a rate of 6.25 Fly Buys points for one airpoint dollar, you'll be a while before takeoff."

The top shopping-voucher rewards scheme was the Farmers card. However, with an annual interest rate of 23.95 per cent, the card has a higher interest than most credit cards.

"Voucher schemes may influence shopping habits, but if you can buy the item more cheaply elsewhere, it makes sense to do that rather than pay extra to earn points."

Ms Chetwin said when comparing rewards schemes, people should consider: the card's annual fee; the reward scheme fee; and for what type of spending the card would be used.

Massey University banking expert David Tripe said it was important to understand that reward points were part of an overall marketing package. "[The banks want] to make their product look attractive relative to other products on the market.

"The overall effect of many of these is to confuse the pricing - make the pricing less transparent. If you make the pricing less transparent, you've got a better chance that someone will pay more for whatever goods they're buying."