Growing Degree Days (GDD) Calculator
GDD quantifies heat accumulation driving crop development. Enter today's high and low temperatures and your crop; the tool gives today's GDD, an estimate of days to reach a target, and a growth-stage hint.
Results
How to Use This Calculator
Select your crop to load its base temperature, enter today's daily high and low from your station or forecast, and the total GDD target (e.g. corn to maturity ~1200-1500). Click Calculate. Repeat daily and sum to track cumulative GDD.
About This Tool
About
Applicability: Applicable to major field crops (corn, soybeans, wheat) in North America and Europe, adaptable worldwide.
How the Calculation Works
Daily GDD = (Tmax + Tmin) ÷ 2 − Base; if negative, set to 0. Corn base 10°C (50°F), wheat 0°C (32°F), soybean 10°C, alfalfa 5°C, grape 10°C. For Tmax 28, Tmin 15, corn (base 10): avg = 21.5, GDD = 11.5. At that rate, reaching 1200 GDD takes ~104 days. Common mistakes: using °F with °C bases, forgetting to floor GDD at 0, and using daily mean without clipping extreme highs/lows (some methods cap Tmax at 30°C).
Reviewed by Agricalc Editorial Team — Agricultural engineers and agronomists with 10+ years of field experience. Our team verifies every calculator formula against peer-reviewed extension publications. For site-specific advice, consult your local agronomist.
References
- NOAA — Growing Degree Days
- Penn State Extension — Growing Degree Days
- USDA Climate Hubs — Crop Development
Frequently Asked Questions
What base temperature should I use?
Use the crop's cardinal minimum: corn, soybean and grapevine 10°C (50°F); wheat and small grains 0°C (32°F); alfalfa 5°C (41°F). Using the wrong base inflates GDD and mis-dates development.
How do I accumulate GDD over a season?
Calculate daily GDD each morning from the previous day's high/low, and sum them from your chosen start date (typically planting or a fixed calendar date). Compare the running total to the crop's known GDD requirements for key stages.
What GDD does corn need to mature?
By adapted maturity, corn needs roughly 1100-1500 GDD (base 10°C, from planting) to black-layer maturity. Shorter-season hybrids finish near 1100; full-season hybrids near 1500. Check your seed tag's GDD requirement.
Does GDD work in °F or °C?
Both, as long as units match the base. °C-GDD = (Tmax°C+Tmin°C)/2 − base°C. °F-GDD = (Tmax°F+Tmin°F)/2 − base°F. They are not equal numerically; 1°C GDD = 1.8°F GDD. Always state which you're using.
Why is my crop ahead of normal this year?
If accumulated GDD is above the long-term average for the calendar date, the crop will be ahead — warm springs accelerate development. Conversely, cool seasons delay it. Using GDD avoids judging progress by the calendar alone.
