Growing Degree Days (GDD) Calculator

Plants don't develop on calendar days. They develop on accumulated heat. GDD predicts crop stage and pest emergence from temperature data.

Calculate accumulated GDD

Crop / pest model

Target Sweet corn Field corn Tomato Pepper Cucumber Snap beans Dry beans Peas Cabbage Broccoli Potato Onion Carrot Wheat Soybean Cotton Wine grapes Apple Strawberry Codling moth (apple pest) European corn borer Cabbage looper Spotted cucumber beetle Japanese beetle — Custom (enter your own thresholds) —

Base temperature (°F)

Upper threshold (°F) Above this, growth doesn't increase further

Day's temperatures

Daily high (°F)

Daily low (°F)

Days at this temperature For estimating accumulation over a stretch

Prior accumulated GDD Carry-over since planting

How GDD works

The basic formula:

GDD = ((T_max + T_min) / 2) − T_base

If the average daily temp is 70°F and the crop's base temperature is 50°F, that day gives 20 GDD. After enough days, the crop has accumulated the heat units it needs to flower, set fruit, or mature.

Modifications used in this widget:

• If T_max exceeds the upper threshold (typically 86°F for warm-season crops), it's capped at the threshold for the average. Heat above ~95°F doesn't accelerate growth. It stresses plants.
• If T_min is below T_base, it's set to T_base for the average (the "single-sine" simplification).
• If the resulting GDD is negative, it's set to zero (no growth on cold days).

Why GDD beats calendar days

Scenario	Calendar days	GDD
Sweet corn, typical year	~75 days from emergence to silk	1400 GDD (base 50°F)
Sweet corn, cool spring	85 days	1400 GDD
Sweet corn, hot summer	65 days	1400 GDD

The calendar varies; the GDD doesn't. This is why pest emergence (codling moth, cucumber beetle, etc.) is also tracked in GDD: the bug needs the same heat units regardless of calendar date.

Common GDD thresholds (base/upper temps)

Target	Base (°F)	Upper	GDD to maturity / event
Sweet corn	50	86	~1400 GDD to silking
Field corn (long season)	50	86	~2700 GDD to physiological maturity
Tomato	50	95	~1300 GDD seed-to-harvest
Pepper	55	95	~1500 GDD
Cucumber	55	90	~600 GDD to first harvest
Snap beans	50	86	~600-700 GDD
Soybean	50	86	~2400-2900 GDD by maturity group
Wheat	32	90	~2200 GDD planting to maturity
Wine grapes (Cabernet)	50	90	~1500-1700 GDD bud-break to veraison
Codling moth (apple)	50	88	First flight ~250 GDD; egg hatch ~430 GDD post-biofix
European corn borer	50	86	First flight ~375 GDD; treatment window ~600-700 GDD

Free under CC BY 4.0. Cite as "Open Agriculture Technology Growing Degree Days Calculator (openagriculturetechnology.com)". Crop GDD thresholds from extension publications and field crop literature.