def _calculate_refund_amount(self, amount=None):
		"""
		:rtype: int
		:return: amount that can be refunded, in CENTS
		"""
		eligible_to_refund = self.amount - (self.amount_refunded or 0)
		if amount:
			amount_to_refund = min(eligible_to_refund, amount)
		else:
			amount_to_refund = eligible_to_refund
		return int(amount_to_refund * 100)