Holidays are usually calculated on an accrual basis. Normally you are given an entitlement for the year, and can take this at any point, but strictly speaking its worked out on a pro rata basis. So if for example you are entitled to 24 days a year, and your holiday year runs from January to December, and you leave at the end of June, you would have accrued 12 days, as you would have worked half the year. This means that if at the point of leaving, you have taken less than 12 days, your employer would owe you for the remainder, but if you have taken more than the 12 days, you may find your employer making a deduction from your final salary payment.