If you’re carrying a balance on multiple credit cards, a smart move can be consolidating to a single balance transfer card. This can also work for outstanding medical bills. The key to doing it wisely, so that you save money, is to minimize the interest you’ll pay.

First, look for cards offering an initial 0% interest period. These promos often last 12 months, but sometimes you can find offers as high as 21 months. These cards are especially valuable for transferring balances you can fully pay off during the 0% period, avoiding all interest on that balance for a year or more.

What if your balances are bigger than you can pay off over the promo period? While you can obviously keep the remaining balance on the card, you’ll be hit with a much higher interest rate after the intro period expires. This later APR may be quite high, and potentially higher than you’re paying on your current cards.

A better idea may be to plan more than one transfer. Pay off as much as you can while you’re in the 0% period, but before the intro expires, do a new balance transfer on what’s left, to a new 0% card.

Alternatively, you could transfer only as much of your balances as you feel confident you can pay off during the 0% period. This at least allows you to avoid all interest on some of your debt.

Sometimes you can find another option: a balance transfer card that offers a low standard interest rate instead of an introductory 0% rate. If your current cards charge 20% on average and you can move the balances to a card offering 11 or 12%, this can still deliver significant cost savings to you over time without having to do another transfer.