CSF Growing Degree Day Calculator

 © Cornell University, 2016. Credits: Tool Developed by Art DeGaetano & Rick Moore.

The Growing Degree Day (GDD) calculator measures heat accumulation to help agricultural producers predict when a crop will reach important developmental stages. It can also be used to help predict potential pest and disease threats. At this time, the GDD tool uses a threshold that was originally optimized for corn production, but it can be suitable for other agronomic crops as well.

Please also take our brief survey to give us feedback on the GDD tool.

How do I use this tool?
1. Select your location by inputting your county, state, zip code, or address after clicking on the “Change Location” field, or by navigating to your desired spot on the pop-up map, after clicking “save and select location”
2. Use the control panel on the left to input your planting date
3. Select your “GDD Threshold” of either base 50 or 86/50 – the graph will automatically update depending on your choice for every parameter
4. Once all your information is chosen, view the graph output
5. Toggle between “Seasonal Outlook” and “Recent Trend” graphs

Once the information in the tool is set, your graph will appear showing GDD accumulations corresponding to the most recent 15-year average, the 30-year (1981-2010) average historical maximum, historical minimum, and this year’s accumulations.  A predicted accumulation is also given based on the weather forecast for the next seven days, and you can toggle to a graph that shows the forecast extended to the end of the growing season based on historical accumulations for the remainder of the growing season.

How does this tool work?
This tool plots Growing Degree Days (GDD), also called Growing Degree Units (GDUs), which measure heat accumulation in order to predict plant and insect development. In a stress-free environment, the development rate of a plant is dependent on temperature. Using the expected temperature of the summer season, based on previous years, this tool can help predict the best days to plant, harvest, and fertilize.

GDDs are calculated by taking the average of the daily maximum temperature and minimum temperature, and then subtracting a base temperature. The base temperature is the lowest temperature at which a crop will grow. For corn and many other crops, this is 50°F, and is the base that the tool uses.  On days when the average temperature is below 50°F, the GDD value is set to zero. Most crops also have a maximum temperature above which growth slows. This temperature is usually approximately 86°F. Thus, the 86/50 degree day method is often used to assess crop development.  In this method 86°F refers to the maximum temperature and 50°F the minimum. In computing these degree days, maximum temperatures above 86°F are set to 86 and minimum temperatures below 50°F are set to 50.  Typically the 86/50 method is used to assess crop development, particularly corn, while the use of only the 50° base temperature is used to track pest appearance.

Producers can use this tool to:
 Make the best selection of crop varieties, optimize planting and harvesting times, etc…
 Respond to sudden changes: to alter planting plans, seed varieties, etc. if unpredictable weather (i.e. heavy rainfall) occurs
 Assess how a particular season compares to historical or future seasons given climate change.

How is our GDD Calculator different from others?
This calculator uses a moving 15-year average of the most recent 15 years to make predictions, and is updated each year to include the most recent data. Other GDD tools use a fixed 30-year average to make calculations, as opposed to the moving 15-year average, which allows the tool to make predictions that might better align with the changing climate and bring you more up to date information to improve your crop yields.

Please note that this tool only covers the Northeastern United States. If you live outside this region, check out other regional GDD tools:
Southeast: AgroClimate.org
Midwest: Useful to Usable
General: The Weather Channel