Growing Degree Day Calculator

One day of heat units from Tmax, Tmin, and crop base. Not a season log of another index.

Formula

Tmax_used = min(Tmax, Tcap)   if a cap is set
Tavg = (Tmax_used + Tmin) / 2
GDD = max(0, Tavg − Tbase)

This is the simple average method used by many US extension services
for corn (50/86 °F). It is not the Baskerville–Emin sine method.

GDD in °F is not the same number as GDD in °C (factor 5/9).

References

1. Nielsen RL. Heat unit accumulation and corn development. Purdue University Extension. Corn 50 °F base, 86 °F cap.
2. USDA / NASS and land-grant extension GDD documentation. Simple daily average with crop-specific Tbase.

Field planning aid only. Confirm rates with your agronomist, label, and local extension. Not a pesticide or fertilizer recommendation.