Heating degree days (HDD) and cooling degree days (CDD) are climatological metrics used to express the magnitude of the heating or cooling load in a given location. These metrics are expressed in terms of a "base temperature" (e.g., "Heating Degree Days Base 65 F"). HDD are calculated by taking the daily average temperature; if it is colder than the "base temperature," the difference is calculated. This difference is summed for the period (week, month, year) in question. Note that cooling season data are often presented in terms of “cooling degree hours” (due to diurnal temperature swings), which are not directly translatable to CDD.