How do credit cards work - when you pay it off

dspr

My next barclaycard payment due date is 21st May.

• I have owed Amount X for months and have now paid it off. (I will also make a payment equivalent to next month's estimated interest over the counter as online banking won't allow me to go into credit)
  
• I then need to make a new purchase worth Amount Y and plan to do this after leaving one clear day after my Amount X (and interest) repayment

When I receive the next bill, will Amount X's interest be part of the bill? Or will the interest only be for Amount Y since I am leaving one clear day between the repayment and new purchase?

pqrdef

They only calculate interest when they make up the statement. Your bill will show

Balance brought forward £X
Payment received £-X
Payment received £-I (estimated interest)
Purchase £Y
Interest £I
Balance £Y

Your minimum payment is calculated on £Y.
There'll be no interest shown on the purchase. If you pay off in full by the due date, there'll be none to pay, otherwise they'll catch up next time and charge interest from the date of purchase.

It makes no difference whether you make the purchase before or after you clear the balance.

Have you got one of those cards where you only get an interest-free period if you paid off the previous statement? Still the same, because you only have to pay the £X by the due date. You don't have to pay the £X before you make the purchase and you don't have to get the balance down to absolute zero at any point.