The benefit of interest free is that the money you would normally spend, actually sits in your bank or savings account until you pay off the credit card (instead of when you buy the product).
If you stick it in a decent account, you get about 45p per £100 per month.
So if you put £500 on a normal card every month, you make £2.25 free (£27 per year)
If you have a 12-month introductory interest free period, then you don't need to pay anything off for 12 months (rather than the normal 1)
If you can avoid paying that £500 for 12 months, then that's £27 per £500 spent (or about £175 in the year!!).
But then you have to be able to pay the whole balance off (in this example, £6,000) at the end of the period.
Otherwise the interest you pay the credit card company swallows up the profit you've made.


There are credit agencies which collect details of what you pay and don't pay.
When you apply for credit in the future (bank accounts, other cards, loans, mortgages, etc.),  the lender will check you out with a credit agency (there are three main ones in the UK).
If you have a record of paying things off, it's better than having no record at all.
Funnily enough, for credit card applications, they actually favour people who miss occasional payments since that'll make them more money (they're businesses, after all).

Does that make sense?

If you have 12 month interest free, and you spend £500 in January then you can leave it on the card until the following December (ie. not pay it off).
That means you have that £500 in your savings account of choice from January to December (instead of it being spent in January).
So you make about £2.25 from it each month, ie. £27 in the year.
The £500 you spend in February, you get 11 months for (ie. about £24.75), and so on.
In a year, that accumulates to about £175 (I think).

So actually the "£27 per £500 spent" only really refers to £500 at the beginning of the term. Sorry if I didn't make sense.
[and by "spent", I meant "put on the card" - technically you've still spent it, but the money's come out your credit card account rather than your operating account]

As but that's where changing cards comes in.

You get a different card, that offers 0% for X Months and 0% balance transfers and a BIGGER limit. So, you keep saving money in your account and use this new card next year, by transfering the old balance to it...... that way you make even more interest!  

OR

You pay of the balance of the old one, and start the process again in January with a new 0% card. Up to you.

The first option means you can get a bigger balance in your account to make interest on (i.e. more than £175) , so will make more money. But means you have more to pay more off at the end.

The second means you will make another £175 in the following year. (assuming interest is the same on your current/savings account)

Companies charge a balance transfer fee of about 2-3% of the balance. So if you transfered your £6000 from year 1, to another card with 0% for 12 months, then you would pay (for 2.5%) £150. Which would be most of your interest. Overall profit would be £25 BUT if you keep this cycle up til you max your limit then you could make a little bit of money..... Maybe.

It's generally just good to put off payments, especailly after xmas.

However, you can only get a card with a large limit with a good credit history and usually a house! My limit is £500. So it's just extra spenging money really!

Didn't know that, shall bear it in mind. I don't have the collateral to be doing that yet though!