The £50... the £450 should be within the interest-free period.
Edit:
Actually it depends on how that £500 ended up on the account. If you put £500 onto the card this month, then there's an interest free period, and you should be paying interest on the £50. If you carried over £500 from previous months, then you'd be incurring interest on the whole £500 for the month.
Edit:
Actually it depends on how that £500 ended up on the account. If you put £500 onto the card this month, then there's an interest free period, and you should be paying interest on the £50. If you carried over £500 from previous months, then you'd be incurring interest on the whole £500 for the month.
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