Growing Degree Days Calculator
Choose a common daily calculation method, enter temperatures and a base threshold, and review the accumulated heat units.
A QUICK WALKTHROUGH
How to use this tool
- Choose the average or minimum/maximum method.
- Enter the temperature, base threshold and optional upper cap in one unit.
- Review daily and cumulative degree days.
Formula and public source
The minimum/maximum method uses max(0, ((Tmax + Tmin) / 2) − base), with an optional user-selected upper temperature cap before averaging. The average method uses max(0, daily mean − base). These are simplified growing degree day calculations; see USDA NRCS, Growing Degree Days: https://directives.nrcs.usda.gov/sites/default/files2/1712930529/25315.pdf .
Model limits
This is a simple thermal-time estimate. Base temperatures, upper thresholds, counting start dates, and crop-stage interpretations vary by crop and method. It does not model hourly temperatures, nonlinear development, dormancy, moisture, or local calibration; use agronomic guidance for decisions.
Local processing
Calculations run in this browser. No weather data is fetched and no input is uploaded or stored.
GOOD TO KNOW
Common questions
Which method should I choose?
Use the method specified by your crop or extension guidance. The calculator offers a daily mean method and a minimum/maximum method; they are not interchangeable for every crop.
Can I enter Fahrenheit and Celsius together?
No. All values in one calculation must use the same temperature unit.
Does this predict a planting or harvest date?
No. It totals supplied observations only and does not provide crop-specific thresholds or forecasts.