Why use this calculator
Growing Degree Days (GDD) provide a more accurate measure of crop development than calendar days because plant growth is driven by temperature accumulation. Tracking GDD helps you predict maturity dates, time fungicide applications, schedule harvest, and compare seasonal progress across different years.
How to use it
Enter the average daily maximum and minimum temperatures, the base temperature for your crop, the number of days elapsed since planting, and the target GDD for crop maturity. The calculator shows daily and accumulated heat units plus estimated days remaining to reach the target.
The formula
GDD per day = max(0, (Daily Max + Daily Min) / 2 - Base Temperature). Accumulated GDD = Daily GDD x Days Elapsed. Common base temperatures: corn 10C, wheat 0-5C, cotton 15.5C.
Worked examples
Max 28C, Min 15C, base 10C, 30 days elapsed, target 1500 GDD
11.5 GDD/day, 345 accumulated, 23% of target reached, approximately 100 days remaining
Max 32C, Min 20C, base 10C, 60 days elapsed, target 1200 GDD
16.0 GDD/day, 960 accumulated, 80% of target reached, approximately 15 days remaining
When people use it
- Predicting crop maturity and harvest timing
- Scheduling growth-stage-specific chemical applications
- Comparing seasonal crop progress between years
- Planning planting dates to meet market timing targets
Tips
- Use actual daily temperature records rather than averages for more accurate tracking
- Different crops have different base temperatures; verify the correct base for your crop
- GDD accumulation slows during cool spells and accelerates during warm periods, affecting maturity predictions
- Many agricultural weather services provide automatic GDD tracking for your location
Questions people ask
- What base temperature should I use?
- Base temperature is the minimum temperature below which a crop does not grow. Common values: corn and soybeans 10C, wheat and barley 0-5C, cotton 15.5C, canola 5C. Using the wrong base temperature will give inaccurate GDD calculations.
- How do I find the target GDD for my crop?
- Target GDD values are published by seed companies and university extension services. For example, corn hybrids typically require 1,200-1,800 GDD from planting to maturity depending on the maturity rating. Check your specific variety's requirements.
- Why use GDD instead of calendar days?
- Calendar days do not account for temperature variation. A crop planted in a cool spring may take more calendar days to mature than one planted in a warm spring, but both will accumulate similar GDD. This makes GDD a more reliable predictor of crop development stage.