Growing Degree Days
Calculator

Growing degree days (GDD) accumulate daily heat units above a crop-specific base temperature (often 50°F/10°C) to track how much "growing warmth" a plant has actually experienced, which predicts development stages more accurately than calendar days alone.

Plant development is driven by accumulated heat, not time itself, so a cool spring delays a plant's progress toward flowering or harvest compared to a warm one, even on the same calendar date. GDD tracks the actual physiological clock the plant is running on.

It's typically the day's average temperature (high plus low, divided by two) minus the base temperature for that crop, with negative values usually treated as zero since temperatures below the base don't contribute to growth.

Each species has a minimum temperature below which its growth essentially stops; cool-season crops like peas have a base around 40°F (4°C), while warm-season crops like corn or tomatoes use a higher base around 50°F (10°C), reflecting their different cold tolerances.

Seed suppliers and agricultural extensions publish target GDD totals for key stages like emergence, flowering, or harvest for specific varieties, so once your accumulated GDD reaches that published threshold, the crop should be at or near that stage regardless of how many calendar days it took.