A variety of formulas are used to calculate degree-days. Most common methods include SIMPLE AVERAGE - this is Tmax+Tmin/2 - threshold. Note that GROWING DDs in our system are the sweet corn formula and ARE NOT the same as SIMPLE AVERAGE. GDDs use a substitution rule: if the Tmin is less than the lower threshold (TLOW), we substitute TLOW instead of Tmin, and if the Tmax is greater than the upper threshold (THI), we substitute THI instead of Tmax in the formula. For more complex formulas and more on degree-days, see this UC Davis IPM webpage.