Growing Degree Days (GDD) Calculator
Calculate daily and cumulative growing degree days (heat units) to predict crop development, maturity, and pest timing.
Results
What is it?
Growing Degree Days (GDD) quantify the heat energy available for crop development above a base temperature (below which no growth occurs). GDD = max(0, (Tmax + Tmin)/2 − Tbase). Accumulated GDD predicts flowering, maturity dates, and pest emergence timing far more accurately than calendar days.
How to use
Enter the maximum and minimum temperature for the day (or average daily temperatures). Select the appropriate base temperature for your crop. Enter the number of days to estimate accumulated GDD (assuming constant daily averages for a forecast period).
Example scenario
Corn planted on May 1. Daily average: Tmax = 28°C, Tmin = 14°C. Tmean = 21°C. GDD/day = 21 − 10 = 11 GDD. Over 90 days: ≈ 990 GDD. Corn silking typically occurs at 860 GDD; maturity at 2,700 GDD — so full-season corn requires about 245 days at this temperature pattern.
Pro tip
Corn hybrids are sold by relative maturity (RM) which approximates the GDD required: a 100-day hybrid needs ≈ 2,500 GDD. In cold regions, choose shorter-season hybrids or switch to spring wheat (faster to mature at lower GDD accumulation). GDD models for pest prediction (aphids, corn earworm, codling moth) allow targeted spray timing that reduces applications by 30–50%.