Growing Degree Days Calculator





Growing Degree Days for Hunwick


Temperature is one of the main driving forces for all biological development and reproduction.

Growing degree days are units of heat energy above a threshold for any day and can be used to estimate the timing of biological processes.

These include the timing of seed germination, bud burst and ripening of crops, as used by gardeners.

Prior to 2000 it was used extensively by farmers for fertiliser application prediction, these days more accurate systems are available.

It can also predict the emerging of dormant insects that rely on heat to survive.


Each plant and animal species have a different base temperature which is the lowest point at which the species is developing
and each stage of the development occurs at different levels of GDD.


One example is Wheat, which has a base temperature of 5.5°C, Emergence at 82 GDD and ripens at 996 GDD.
This all starts from the date of planting, which in the case of winter wheat is in the autumn so it starts growing before the cold weather
then becomes dormant until the temperature begins to rise above 5.5°C again.


GDD is calculated using the daily max and min temperature, when this temperature is above the base temperature, the total GDD
begins to accumulate. the basic formula is GCC = (Tmax + Tmin)/2 - Tbase. if Tmin < Tbase then Tmin = Tbase.


To use the calculator you must first know the development data for the species (base temperature, growth rate etc.)
then enter the planting date or 1 Jan. for insects, then select the base temperature and press 'Calculate'
you can then use the GDD figure to estimate the growth stage of the species from your data.