During Christmas and new year 1999-2000 there will be eight bank holiday or weekend days. Emergency admissions are likely to be high during this period. A mathematical model can be used to calculate how many beds will need to be empty on Christmas day in order to cope with an increase in emergency admissions afterwards. In this study of a 781-bed acute hospital, a minimum of 209 beds--equivalent to seven wards--will need to be empty on Christmas day. This model is derived from information on the patient administration system and could be used by all hospitals to plan care.